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Question: what will the first-round margin between the top two presidential candidates in São Tomé e Príncipe be (by August 12, 2026)? Forecasters agree the main driver is candidate-field fragmentation in a small, personalistic two‑round system and that recent competitive first-round margins have clustered in the low‑teens to mid‑20s (e.g., ~18.7 pp in 2021, ~25 pp in 2016, ~13–15 pp in 2001/2011), with a single near‑tie precedent in 1996. Given ADI’s organizational strength (incumbent Carlos Vila Nova eligible; ADI won 2022 legislative elections) the teams center the distribution in the high‑teens (around 18–20 pp) but emphasize meaningful tails: a compressed single‑digit margin if opposition parties and independents coalesce, and a larger 20–30+ pp lead if the opposition remains fragmented. All models assign only a small probability to an extreme >45 pp first‑round gap as historically atypical. Forecasters also note procedural risk (postponement or delayed certification could void the question) and recommend updating once the official candidate list and any polling appear.
Forecast: Probability distribution:
Key drivers of the first-round 1st-vs-2nd margin in São Tomé e Príncipe are (1) how fragmented the final candidate field is, (2) whether the ADI-aligned electorate consolidates behind one option or stays split between rival ADI-associated candidacies, and (3) whether the opposition coalesces around a single strong challenger. Recent historical anchors suggest margins commonly land in the mid-teens to mid-20s (e.g., ~14 pp in 2011, ~20 pp in 2021, ~25 pp in 2016), but there is precedent for much tighter outcomes in older elections and a plausible 2026 path to a compressed three-way race if ADI and/or opposition votes split in an unusually balanced way. Conversely, if one candidacy emerges as clearly dominant while challengers remain fragmented, margins can push into the 30s or low 40s. Given limited poll data and meaningful uncertainty about final candidate consolidation as of 2026-06-02, I center the distribution around the mid-teens while keeping a substantial lower tail for a near-tie scenario and an upper tail for a dominant front-runner scenario. I assign <1% probability to an extreme blowout exceeding 45 pp, so I keep p99 below the open upper bound.
An amateur forecast is likely to anchor on the last election’s ~20 pp margin (or a simple historical average) and underweight (a) the unusually salient party-splitting dynamics discussed by multiple analysts and (b) the genuine possibility of a tight top-two gap in a small electorate with shifting alliances. My forecast improves calibration by explicitly widening the lower tail (non-trivial chance of <5 pp) while still respecting the historical tendency for double-digit spreads, and by avoiding artificial pile-up near the 45 pp cap.
Forecast rationale (numeric):
— Iteration 1 — Overall, the forecasts converge on a moderate first-round lead for the frontrunner, with the margin most likely in the mid-teens to around 20 percentage points. The main reasoning pattern is:
There is some spread in the central estimate: one view emphasizes a smaller, historical-average margin around 10–11 points, while others lean more toward a mid-teens to high-teens lead. But there is broad agreement that the distribution is right-skewed: a near-tie is possible, yet so is a much larger margin if the opposition remains divided.
— Iteration 2 — Across the forecasts, the main benchmark is the 2021 first-round margin of 22.6 percentage points, which is used as the central historical anchor. The overall expectation is that São Tomé and Príncipe’s first-round field will remain fragmented enough to give the front-runner a clear lead, but not necessarily an overwhelming one.
The collective reasoning points to a moderate first-round lead, most likely around the low-to-mid 20 percentage-point range, with downside risk if the opposition unites and upside risk if fragmentation or boycott dynamics become severe.
— Iteration 3 — Across the forecasts, the main drivers are:
The shared view is that the first-round gap is most likely to be meaningful but not extreme, with a central tendency somewhere around the high teens to low 20s percentage points.
The main disagreement is about how much the record fragmentation will compress the margin:
The collective reasoning points to a first-round lead in the high teens or low 20s, with a plausible downside toward a close race if fragmentation is especially strong, and an upside toward a larger gap if the leading candidate consolidates support.
Summary of Forecasting Rationales
The consensus across the forecasting rationales is that the first-round margin between the top two candidates will likely be notably narrower than historical averages due to severe intra-party fracturing, though a reversion to traditional wide margins remains a credible alternate scenario.
Historical Precedent (The Outside View) Historically, São Tomé and Príncipe’s two-round electoral system has produced wide, double-digit margins in the first round. The electorate traditionally consolidates around the frontrunners of the two dominant political forces—the center-right ADI and the center-left MLSTP-PSD—allowing the first-place candidate to secure a commanding lead over the runner-up.
The 2026 Political Crisis (The Inside View) Forecasters universally point to a profound institutional rupture that disrupts this historical baseline. Incumbent President Carlos Vila Nova’s recent dismissal of his own party’s Prime Minister, Patrice Trovoada, has caused an unprecedented schism within the ruling ADI. Consequently, the traditionally unified center-right base is expected to heavily fracture between Vila Nova loyalists and a challenger backed by Trovoada’s formal party machinery.
Opposition Splintering and Third Parties This vote-splitting dynamic extends beyond the ruling party. The main opposition, MLSTP-PSD, faces internal divisions and independent pre-candidacies that threaten to dilute its traditional base. Additionally, viable third-party movements are positioned to capture voter frustration over economic headwinds and political volatility.
Synthesized Scenarios Forecasters balance two primary outcomes:
Question: By how many percentage points will the first-place candidate lead the second-place candidate in the first round of São Tomé e Príncipe’s July 19, 2026 presidential election? Final Prediction: Probability distribution:
Total Cost: extra_metadata_in_explanation is disabled Time Spent: extra_metadata_in_explanation is disabled LLMs: extra_metadata_in_explanation is disabled Bot Name: extra_metadata_in_explanation is disabled
Forecaster 1: Probability distribution:
Forecaster 2: Probability distribution:
Forecaster 3: Probability distribution:
The research brief notes the first-round presidential election in São Tomé e Príncipe is scheduled for July 19, 2026 and, as of June 2, 2026, at least three candidates had declared or filed (incumbent Carlos Vila Nova (ADI), ADI parliamentary leader Nito Viegas D’Abreu, and independent Miques João Bonfim), with the candidacy deadline on June 4, 2026. There are no available public polls or active prediction-market contracts for this race. The dominant ADI party is undergoing a serious internal split (including the launch in May 2026 of a new party, “Nossa Terra,” by ADI dissidents), ongoing disputes over party control, and wider country issues (energy/water crises, modest economic growth); these dynamics create major uncertainty about vote consolidation and final candidate fields.
Using historical base rates, the brief summarizes first-round margins from prior elections (1996: 4.63 pp; 2016: 25.05 pp; 2021: 18.8 pp) and notes that larger candidate fields and fragmentation tend to increase margins between first- and second-place finishers while incumbent advantage and fragmented opposition also push toward larger margins. It lists structural factors favoring larger margins (incumbency, opposition fragmentation, multi-candidate field) and factors favoring smaller margins (ADI division, public discontent, generational appeal of challengers, new-party competition). The brief’s reference-class analysis highlights 2021 (18.8 pp margin, 19 candidates) as the closest comparator and concludes—subject to significant uncertainty due to unknown final candidate count, ADI unity, Patrice Trovoada’s role, and lack of polling—that historical base rates imply a likely margin in the roughly 10–25 percentage-point range, with a most-likely scenario around 15–20 percentage points. Critical uncertainties and the two-round electoral system (50%+ needed to win outright) are explicitly noted.
Sources used (as listed in the brief): news reports (May 2026) [1][2][3]; Tribunal Constitucional (official certified results); Comissão Eleitoral Nacional (CEN) (provisional results); African Union and ECOWAS election observation missions [4][5]; Polymarket (searched; no active markets found) — https://polymarket.com; and the brief’s internal references [6][7][15][16][17][19][21][25][26][27].
The first round of São Tomé e Príncipe’s presidential election is scheduled for July 19, 2026. This will be the country’s eighth democratic presidential election cycle. The question asks for the margin in percentage points between the first-place and second-place candidates in the first round.
Based on news reports from May 2026, at least three candidates have officially declared or filed their candidacies [1][2][3]:
The deadline for candidacy submissions was June 4, 2026 [1][2], so additional candidates may have emerged after the news coverage in mid-May.
Historical margins between 1st and 2nd place in first-round voting:
The dominant ADI party is experiencing a severe internal split [25][26]:
No specific prediction markets or polls found for this election. My search of Polymarket and similar platforms yielded no active markets for São Tomé e Príncipe’s 2026 presidential election [21]. This reflects the small size and limited international attention to São Toméan elections.
Most comparable election: 2021
Key difference: In 2021, Vila Nova was the opposition challenger running against the ruling party. In 2026, he is the incumbent, which typically provides advantages but also makes him the target of anti-establishment sentiment.
Resolution sources (in order of priority):
All must publish before August 12, 2026 for question resolution.
Bottom Line for Forecasters: Based on historical base rates, expect a margin in the 10-25 percentage point range, with the most likely scenario around 15-20 percentage points given the expected multi-candidate field and political fragmentation. However, significant uncertainty exists due to lack of polling, unknown final candidate count, and unprecedented ADI party crisis. The 2021 election (18.8pp margin, 19 candidates) provides the strongest reference class.
Conditional forecast on the question not being annulled.
(a) Time left until the outcome is known.
Today is June 2, 2026. The first round is scheduled for July 19, 2026, so there are 47 days until voting; the question’s publication cutoff is August 12, 2026, 71 days away. The CEN site also lists the 2026 presidential election date as 2026-07-19. (stpcen.st)
(b) Outside view: reference class and base rates.
For São Tomé e Príncipe’s competitive multiparty presidential first rounds since 1996, first-vs-second margins have usually been in the mid-teens to low-20s: 1996: 4.63 pp, 2001: 15.20 pp, 2006: 21.76 pp, 2011: 13.83 pp, 2016: about 25.0 pp, and 2021: about 18.8 pp. That gives an approximate mean of 16.5 pp, median around 17.0 pp, and recent-cycle average around 19 pp. (en.wikipedia.org)
(c) Inside view: case-specific evidence.
The incumbent, Carlos Vila Nova, has formally filed and is running as an independent on stability/continuity; as of May 29, Vila Nova and Miques João Bonfim were the only formalized candidacies reported, though the deadline is June 4. (rstp.st) Nito Viegas d’Abreu, the ADI parliamentary leader, has announced, and Domingos “Nino” Monteiro announced on June 1, increasing the likelihood of a fragmented field. (glebatv.st) The biggest downward update from the base rate is the severe ADI split after Vila Nova dismissed Patrice Trovoada’s government; DW described ADI as divided into pro-government and pro-Trovoada blocs. (amp.dw.com) The biggest upward update is that the MLSTP leadership reportedly chose not to present its own presidential candidate, and MDFM/UL announced support for Vila Nova, both of which reduce the chance of a single strong non-incumbent challenger. (rstp.st)
(d) Outcome if nothing changed.
If the apparent lineup holds—Vila Nova, Nito Abreu, Miques Bonfim, Nino Monteiro, and perhaps a few smaller candidates, with no official MLSTP candidate—I would expect Vila Nova to lead the first round, but not dominate: roughly 36–41% for first place versus 20–26% for second place, for a margin around 15–17 pp.
(e) Outcome if the current trend continued.
If fragmentation continues but the anti-incumbent vote does not coordinate, the leader’s margin could remain in the high teens. If the trend of ADI factional conflict intensifies and Nito becomes the focal challenger for Trovoada/MLSTP-leaning voters, the margin moves lower, more like 8–14 pp. Netting these, I treat the current trend as slightly below the historical base rate.
(f) Expectations of experts and markets.
I have not found usable public polling or a liquid prediction market for this specific first-round margin. Local coverage is mostly about candidacy filings, party splits, and institutional process rather than vote-share forecasts, so I give market/expert expectations little independent weight.
(g) Unexpected low-outcome scenario.
A low margin occurs if Nito Abreu becomes the clear anti-Vila Nova candidate, the Trovoada ADI wing mobilizes strongly, MLSTP voters tactically support him, and Nino/Miques underperform. Then the top two could be around 30–29 or 31–27, producing a 0–5 pp margin.
(h) Unexpected high-outcome scenario.
A high margin occurs if Vila Nova captures the “stability” vote, MDFM/UL support helps him consolidate moderates, MLSTP stays out and its voters split/abstain, while Nito, Nino, Miques, and others divide the challenger vote. Then Vila Nova could be near 45–50% while second place is in the teens, producing a 28–38 pp margin.
Rationale.
I anchor on the São Toméan base rate of roughly 17 pp for competitive multiparty first rounds. The 2021 election, with many candidates and a strong ADI-backed Vila Nova, produced an ~18.8 pp first-round margin, while 2016 produced an unusually large ~25 pp margin because the ADI-aligned first-place candidate nearly reached 50%. The 2026 setup is less clean: Vila Nova has incumbency and some third-party support, and the reported absence of an MLSTP candidate helps him; but the ADI rupture creates a much more credible intra-right/ADI challenger than in a normal incumbent race. I therefore set the median a bit below the recent-cycle average but close to the long-run median: 15.8 pp, with a wide lower tail for a consolidated anti-incumbent challenge and a high tail for opposition fragmentation.
Percentile 0.1: 0.20
Percentile 1: 0.85
Percentile 5: 2.50
Percentile 10: 4.50
Percentile 20: 7.80
Percentile 30: 10.50
Percentile 40: 13.10
Percentile 50: 15.80
Percentile 60: 18.30
Percentile 70: 21.20
Percentile 80: 24.80
Percentile 90: 30.50
Percentile 95: 35.50
Percentile 99: 42.50
Percentile 99.9: 44.90
Conditioning: I am forecasting conditional on the question not being annulled: i.e., the election is held by July 25, 2026, and a valid resolution source publishes results before August 12, 2026.
(a) Time left until the outcome is known.
Today is June 2, 2026. The first round is scheduled for July 19, 2026, so voting is in 47 days; the resolution deadline is August 12, 2026, in 71 days. The election date was fixed by presidential decree, with presidential elections on July 19 and legislative/regional/local elections on September 27. (glebatv.st)
(b) Outside view: reference class and base rates.
The best reference class is contested São Tomé e Príncipe presidential first rounds since 1996. Approximate first-vs-second margins were: 1996 ~4–5 pp, 2001 15.2 pp (55.18% vs 39.98%), 2006 ~21–22 pp (about 60% vs 38.5%), 2011 ~13–15 pp, 2016 ~25.0 pp (49.88% vs 24.88%), and 2021 18.72 pp (39.47% vs 20.75%). This gives a rough historical mean around 16–17 pp, median around 16–18 pp, with the main observed competitive range about 5–25 pp. (es.wikipedia.org)
(c) Inside view: evidence updating away from base rates.
The main upward-pressure evidence is fragmentation: incumbent Carlos Vila Nova has formalized his candidacy, Miques João Bonfim has also formalized, Nito Viegas D’Abreu has announced, and Nino Monteiro announced on June 1, making a multi-candidate field likely. (rstp.st) Vila Nova also received support from MDFM/UL on June 2, a signal that some smaller-party elites may prefer stability/continuity around the incumbent. (rstp.st) The main downward-pressure evidence is the severe ADI split after Vila Nova dismissed Patrice Trovoada’s government in January 2025, plus the Constitutional Court later declaring that dismissal unconstitutional; this creates a plausible path for an anti-incumbent or ADI-factional candidate to keep the race close. (euronews.com) Economic and service-delivery discontent, especially the continuing energy/water crisis, also makes a dominant incumbent margin less secure. (amp.dw.com)
(d) Outcome if nothing changed.
If the race stayed close to the current known/announced field, I would expect Vila Nova to lead the first round, but with Nito, Nino, Miques, and possible late/party-linked candidates dividing the non-incumbent vote. That points to a margin around 15–18 pp.
(e) Outcome if the current trend continued.
The recent trend is more challengers entering while at least one minor party publicly backs Vila Nova. If that continued—more fragmented opposition, no single consolidated challenger—I would move the margin upward to around 18–24 pp.
(f) Expectations of experts and markets.
I found no usable public polling or liquid prediction market for this specific margin. The practical “market signal” is therefore candidate/party behavior: multiple announced challengers, incomplete formal filing as of June 2, and at least one minor-party endorsement of the incumbent.
(g) Unexpected low-outcome scenario.
A low outcome occurs if the anti-Vila Nova vote consolidates late—e.g., MLSTP and the Trovoada-aligned ADI wing tacitly or explicitly coordinate behind Nito or another credible candidate—while the energy/water crisis sharply hurts the incumbent. Then the top two could be something like 31%–29%, resolving near 2 pp.
(h) Unexpected high-outcome scenario.
A high outcome occurs if Vila Nova remains the only broadly acceptable establishment/stability candidate while Nito, Nino, Miques, MLSTP-linked independents, and other late entrants divide the rest. Then Vila Nova could approach 45–50% while the runner-up is near 15–18%, producing a margin above 30 pp.
Rationale.
I anchor on the historical São Toméan first-round base rate of roughly 16–17 pp. The current race has two offsetting features: ADI’s internal crisis and public-service discontent make a close race more plausible than in a normal incumbent reelection, but the expanding candidate field and Vila Nova’s minor-party support make a fragmented opposition and a larger plurality margin more likely. Net, I keep the median slightly below the historical median, around 15.6 pp, but with a wide upper tail because a fractured first round can easily create a 25–35 pp lead.
Percentile 0.1: 0.20 Percentile 1: 0.90 Percentile 5: 2.60 Percentile 10: 4.40 Percentile 20: 8.20 Percentile 30: 11.00 Percentile 40: 13.30 Percentile 50: 15.60 Percentile 60: 18.10 Percentile 70: 21.30 Percentile 80: 25.40 Percentile 90: 31.20 Percentile 95: 36.10 Percentile 99: 42.60 Percentile 99.9: 48.00
All forecasts below are conditional on the question not being annulled: i.e., the election is held by July 25, 2026 and an eligible results source publishes by August 12, 2026.
(a) Time left. As of June 2, 2026, there are 47 days until the scheduled first round on July 19, 2026, and 71 days until the August 12, 2026 resolution-source deadline. The election date was fixed by Presidential Decree 02/2026. (e-global.pt)
(b) Outside view. The best reference class is São Tomé e Príncipe’s multiparty presidential first rounds since 1996. The top-two first-round margins were about 4.63 pp in 1996, 15.20 pp in 2001, 21.76 pp in 2006, 13.83 pp in 2011, 25.05 pp in 2016, and about 22.6 pp in the certified 2021 result. That gives a mean near 17.2 pp and a median near 18.5 pp. Note that the 2021 certified result is higher than some provisional summaries because the Tribunal Constitucional confirmed Vila Nova at 43.3% and Posser da Costa at 20.7%. (en.wikipedia.org)
(c) Inside view. The confirmed/visible field points to an incumbent-versus-intra-ADI-challenger race: Carlos Vila Nova has launched his reelection bid; Nito Viegas D’Abreu, ADI parliamentary leader, has also declared; and Miques João Bonfim is in the field, with candidacy submissions due June 4. (rtp.pt) The ADI split is real and margin-compressing: DW reported that the ADI expelled six pro-government deputies from its parliamentary group and that the party is split between a Trovoada-loyal wing and a pro-current-government wing. (amp.dw.com) There is also anti-incumbent pressure from prolonged electricity/water shortages. (amp.dw.com) Offsetting that, incumbency, name recognition, and possible fragmentation among anti-Vila Nova alternatives push the margin upward.
(d) Outcome if nothing changed. If the race stayed roughly as currently visible—Vila Nova, Nito D’Abreu, Miques Bonfim, plus only weak additional candidates—I would expect the first-place candidate to lead by about 16 pp.
(e) Outcome if the current trend continued. If the current trend of fragmentation continued, with more minor candidates and no unified anti-incumbent bloc, I would move slightly higher, toward 17–19 pp.
(f) Expectations of experts and markets. I found no reliable public polling or liquid prediction market for this election. Qualitative reporting emphasizes ADI’s internal rupture and service-delivery frustration, but does not provide a numerical consensus.
(g) Unexpected low-outcome scenario. A low margin could occur if the official ADI machine unifies behind Nito D’Abreu, MLSTP or another bloc fields/backs a strong candidate, and Vila Nova’s vote is weakened by the energy/water crisis, leaving the top three clustered around the mid-20s to low-30s. That could produce a margin of 0–6 pp.
(h) Unexpected high-outcome scenario. A high margin could occur if Vila Nova becomes the de facto candidate of a broad anti-Trovoada/current-government coalition while the Trovoada/ADI side and smaller parties fragment. In that case the winner could approach or exceed 50% while second place remains in the teens, producing 30+ pp.
Rationale. I start from the historical São Toméan first-round base rate: margins usually land in the mid-teens to low-20s, with a mean around 17 pp. The 2022 legislative result shows the two largest partisan reservoirs were ADI at 46.88% and MLSTP/PSD at 32.73%, but the 2025–26 rupture means those reservoirs may not transfer cleanly into presidential blocs. (eleicoes.stpdigital.net) Relative to the base rate, the ADI split and utility crisis increase the chance of a close, low-margin first round; incumbency and likely candidate fragmentation increase the chance of a large lead. I put the median modestly below the recent 2016/2021 margins but near the long-run base rate: about 16 pp, with a wide right tail but little probability above 45 pp.
Percentile 0.1: 0.20 Percentile 1: 1.20 Percentile 5: 4.00 Percentile 10: 6.20 Percentile 20: 8.80 Percentile 30: 11.30 Percentile 40: 13.60 Percentile 50: 15.70 Percentile 60: 17.90 Percentile 70: 20.50 Percentile 80: 23.80 Percentile 90: 28.10 Percentile 95: 32.50 Percentile 99: 39.50 Percentile 99.9: 44.80
Modal: 16.9-22.5 (27.0%) • partial_shift • 5m56s
Reading: strict
The resolution criteria specify a precise hierarchy of sources (TC → CEN → AU/ECOWAS), a specific denominator (votos válidos only), explicit exclusion of preliminary results, and hard deadlines — leaving little room for interpretive latitude. The rules are tightly defined with multiple explicit edge-case provisions already baked in, warranting a strict reading.
Total evidence registered (shared pool): ?
| Variant | Perspective | Model | Turns | Tools | Status |
|---|---|---|---|---|---|
| 0 | inside_view (inside_view_v1) | anthropic/claude-sonnet-4-6 | 20 | 36 | OK |
| 1 | outside_view (outside_view_v1) | anthropic/claude-sonnet-4-6 | 16 | 28 | OK |
| 2 | contrarian (contrarian_v1) | anthropic/claude-sonnet-4-6 | 24 | 37 | OK |
Evidence confidence: medium
high evidence]Vila Nova’s incumbency advantage and name recognition translate into a clear first-place finish. ADI split costs him some votes to Nito Abreu but not enough to make the race very tight. MLSTP-PSD absence or weak alternative candidates prevent a strong second-place challenger from emerging. Historical base rate suggests margins in this range are common.
ADI split is deeper than expected and Nito Abreu draws heavily from Vila Nova’s support, compressing the margin. Or an unexpected strong candidate (e.g., MLSTP-PSD belatedly fields Elsa Pinto) emerges in second place close to Vila Nova.
medium evidence]MLSTP-PSD absence (per sources 15–16, 30) removes the traditional strongest opposition candidate. The large 18-candidate field (source 17) fragments remaining opposition votes across many minor candidates. Nito Abreu proves weak, leaving Vila Nova with an outsized plurality similar to 2016 (25+ pp margin, source 6).
ADI split means Vila Nova loses a significant portion of ADI’s traditional base to Nito Abreu. A credible unified opposition candidate emerges to consolidate anti-incumbent vote.
medium evidence]The ADI split between Vila Nova and Nito Abreu is severe, with Trovoada actively campaigning for Abreu (source 10) and directing ‘unprecedented verbal violence’ at Vila Nova (source 21). If ADI’s organized machinery backs Nito Abreu effectively, Vila Nova’s vote share is sharply reduced, potentially making the margin very small. A strong independent (e.g., Elsa Pinto with MLSTP support) could also compress the gap.
Historical margins have never been below ~14 pp in recent elections; even in the competitive 2011 race the margin was ~13.8 pp. Incumbency typically provides a structural floor for Vila Nova’s vote share.
low evidence]Severe political instability (constitutional crisis, ADI fracture) leads to postponement. Or election occurs but TC/CEN certification is delayed past August 12 and no AU/ECOWAS observation mission publishes qualifying results in time.
Election date confirmed by presidential decree (source 3). São Tomé has a strong track record as a stable democracy. AU/ECOWAS observation missions typically publish press releases within days of elections.
inside_view_v1)Inside-View Causal Analysis
Current state → causal chain → outcome:
The key structural facts driving my forecast:
Historical base rates (high evidence): Random-walk projection anchored at ~18.7 pp median, with p5≈1 pp and p95≈37 pp (sources 18, 23). Three elections: 2011≈13.8pp, 2016≈25.3pp, 2021≈18.7pp — mean ~19pp, SD ~5-6pp across elections.
ADI split (medium evidence strength, but consequential): Vila Nova fired PM Trovoada (declared unconstitutional, source 14), splitting ADI. ADI officially backs Nito Abreu while Vila Nova runs independent. Trovoada directing “unprecedented verbal violence” at Vila Nova (source 21). This creates a genuine three-way competitive dynamic that could compress the margin compared to 2021.
MLSTP-PSD likely absent (medium evidence): No MLSTP submission as of May 29, 2026 candidacy deadline (source 30). MLSTP came 2nd in 2021 (~20-22% of valid votes). Their absence removes the traditional strongest opposition but doesn’t automatically consolidate behind either Nito Abreu or Vila Nova — it redistributes those votes across the fragmented field, potentially keeping the 2nd-place finisher weak.
18 total candidacies filed (source 17): Very fragmented field. In 2021, 19 candidates still allowed Vila Nova to lead with ~39%. Fragmentation historically doesn’t compress the winner’s plurality dramatically in STP.
Scenario weighting:
Moderate margin 11-25 pp (bins 2-4):
relative_evidence_strength: high. Random-walk median at ~18.7pp; historical precedent strongly in this range. Probability: ~50%.Wide margin >25 pp (bins 5-8):
relative_evidence_strength: medium. MLSTP absence removes strongest opposition; 18-candidate fragmentation could let Vila Nova win by a wider margin. But ADI split counters this. Probability: ~25%.Narrow margin <11 pp (bins 0-1):
relative_evidence_strength: medium. ADI split is real and severe — Trovoada’s party machinery backing Nito Abreu could genuinely make this competitive. Historical floor is ~13.8pp but novel structural factors could push below. Probability: ~20%.Annulment (low evidence): Election confirmed by decree, STP stable democracy, AU/ECOWAS will publish quickly. Probability: ~5%.
Distribution shape: Center mass on bins 2-4 (11-28 pp), with modest tails in both directions. The annulment risk means I must NOT put annulment probability in it’s a void, not a low value (bin_0). However, 0-5.6pp (bin_0) can still receive some genuine low-margin probability from the narrow-margin scenario.
Bin allocation:
- 0-5.6 (bin_0): 5% (annulment ~5% + some genuine very narrow margin probability; combined ~7%, but annulment is not a low value per rules — annulment risk should NOT add mass to bin_0. Adjusting: just genuine narrow margin probability ≈5%)
- 5.6-11.3 (bin_1): 10% (narrow margin scenario bulk)
- 11.3-16.9 (bin_2): 18% (lower moderate range)
- 16.9-22.5 (bin_3): 20% (core historical average range)
- 22.5-28.1 (bin_4): 17% (upper moderate range)
- 28.1-33.8 (bin_5): 12% (wide margin scenario)
- 33.8-39.4 (bin_6): 8%
- 39.4-45 (bin_7): 5%
45 (bin_8): 5%
Total: 5+10+18+20+17+12+8+5+5 = 100%. ✓
The annulment risk (~5% per low evidence) should technically be excluded from the bin distribution since annulment voids the question. I’ve kept bin_0 at 5% for genuine narrow-margin probability only, not double-counting annulment there.
outside_view_v1)Reference class: São Tomé e Príncipe recent presidential first-round 1st-vs-2nd margins (2011 ≈13.8 pp; 2016 ≈25.1–25.3 pp; 2021 ≈18.7–19.8 pp). Base-rate central tendency: ~19 pp (per sources 1, 6, 12, 18, 23). Adjustment: +/– small spread (wider tails) to reflect medium-quality evidence of an unusual 2026 structure — a split in ADI (Trovoada backing Nito Abreu vs. incumbent Vila Nova) and uncertainty about whether MLSTP-PSD ultimately fielded a candidate (sources 7, 10, 15, 30). I treat the brief’s high-evidence scenario (“Moderate margin 10–25 pp”) as the dominant outcome and therefore place most mass in 16.9–22.5 (bin_3) consistent with the historical median and the random-walk projection (median ≈18.7 pp, p5–p95 wide; sources 18, 23). Weighting by relative_evidence_strength: the high-evidence scenario (moderate margin) receives the bulk of probability (0.62 in bin_3); the two medium-strength scenarios (narrow <10 pp and wide >25 pp) receive modest probability shifted into adjacent bins (bin_2 and bin_4, plus small mass in bins 0–1 and 5) to reflect credible but weaker routes to compression or blowout (sources 7, 10, 14, 17, 21). Annulment risk (question void if no qualifying source or postponement) is noted in the brief but judged low-probability and therefore not allocated as explicit mass; the distribution instead preserves probability across numeric outcomes. Confidence in evidence: medium (per brief), so I keep a concentrated center near the historical mean but widen tails relative to a single-point inside view. Numerical breakdown: small chance (0.03) for very narrow margins (0–5.6 pp; reflects p5–p10 tail and severe three-way split risk), modest chance (0.05) for 5.6–11.3 pp, moderate chance (0.16) for 11.3–16.9 pp, dominant chance (0.62) for 16.9–22.5 pp (historical center), smaller chance (0.11) for 22.5–28.1 pp (wide plurality route if opposition fragmented or MLSTP absent), and residual (0.03) for 28.1–33.8 pp. This distribution follows the brief’s scenario weighting (high evidence → majority mass; medium evidence → meaningful but smaller mass; low-evidence annulment scenario not given explicit mass).
contrarian_v2)Adversarial reading
The bulk of the evidence in the brief pulls toward a moderate first-round margin of roughly 10–25 pp (centered on the historical ~19 pp mean from 2011/2016/2021), with the high-evidence scenario explicitly anchored to the random-walk median of 18.7 pp and the three-election average.
Counter-evidence found (or absence)
The ADI split between Vila Nova and the Trovoada-backed Nito Abreu (confirmed by sources 7, 10, 13, 14, 21) is an unprecedented fracture inside the ruling party, accompanied by “unprecedented verbal violence” and a Supreme Court ruling that Vila Nova violated the constitution. This dynamic is absent from the historical sample and supplies medium-strength evidence that the 2026 margin could be materially narrower than the base-rate projection.
Distribution implications
Relative to a naive historical-centroid distribution, extra mass is shifted into bin_1 and 5.6–16.9 pp (bin_2) at the expense of bin_3–bin_5, because the ADI split supplies a concrete mechanism—absent in prior cycles—for compressing the gap between first and second place. The low-evidence annulment scenario receives negligible weight, and the high-evidence moderate scenario still dominates the middle bins but is tempered by the counter-evidence above.
Strategy: logit_mean • Drafts: 3/3
anchoring_v1The draft rationale anchors the p50 squarely at the historical mean of ~18.7 pp (bin_3: 16.9–22.5), which looks reasonable on the surface, but the wide-margin scenario (>25 pp) receives only ~20% combined mass despite two concrete mechanisms that favor it: (1) MLSTP-PSD’s likely absence removes the candidate who captured ~20-22% in 2021 and historically served as the main second-place challenger, and (2) the 18-candidate fragmented field with a dominant incumbent mirrors the 2016 structure (where the margin was ~25 pp). The brief explicitly tags the narrow-margin scenario as supported by “unprecedented verbal violence” and Trovoada’s party machinery backing Nito Abreu, but the ADI split actually means Vila Nova’s chief competition comes from within the former governing coalition — the second-place finisher would be Nito Abreu drawing from the same pool, which could still leave a large gap versus Vila Nova if MLSTP voters scatter across minor candidates. The draft’s outside-view variant concentrates 62% of mass in a single bin (bin_3: 16.9–22.5), treating it as far more likely than a flat-prior reading of three data points and ambiguous structural factors would justify — this is a textbook case of placing peak mass at the optimistic end of the “near-historical-average” range rather than distributing appropriately across the moderate and wide-margin scenarios.
ceiling_v1The key structural ceiling constraint here is the answer range itself: the question states “resolved value is a number in the range 0.0 to 45.0 (closed lower / open upper bound).” This means “Above 45” (bin_8) is structurally excluded — the resolution criteria cap the measurable outcome at 45 pp. Any mass in currently ~0.41% (bin_8) represents outcomes that cannot resolve within the stated range. Additionally, there is a soft upper constraint: if Vila Nova leads with ~50% and second place has ~5%, the margin would be ~45 pp, but that would require a near-majority incumbent in a fragmented 18-candidate field — historically, even the 2016 winner who hit 50.1% only achieved a ~25.3 pp margin because second and third place clustered near 24–25%. The highest observed margin in recent STP history is ~25.3 pp (2016, source 6), and the random-walk p95 is only ~36–39 pp (sources 18, 23), suggesting mass in bins 7 (39.4–45) and 8 (>45) is structurally overcrowded relative to the ceiling evidence.
math_v1The forecast distribution sums to 1.0 and the modal bin (bin_3: 16.9–22.5 pp at 0.376) is reasonably placed at the historical median of ~18.7 pp. However, the distribution exhibits a notable inconsistency: the rationale describes an “inside-view” allocation emphasizing the ADI split and narrow-margin risk (bin_1: 10%, bin_2: 18% for a combined ~28% below 16.9 pp), yet the published distribution places only ~16% in bins 0–2 combined. This under-weights the “medium-strength” medium-evidence scenarios described in the brief and rationale relative to stated conditional probabilities.
Reviews consumed: 3
The draft over-concentrated mass at the historical median (bin_3 ~37.6%) largely due to the outside-view variant’s 62% spike there. The ceiling reviewer correctly flagged that >45 pp (bin_8) is structurally excluded by the stated answer range (0.0–45.0, open upper) and that bins 6–7 are empirically rare — I zeroed bin_8 and trimmed bins 6–7. The anchoring reviewer pushed for shift_higher citing MLSTP absence as a wider-margin mechanism; I partially accepted by keeping meaningful (but not large) mass in bins 4–5, since the 2016 analogue is real. The math reviewer flagged that the published draft under-weights narrow-margin scenarios (bins 0–1) relative to the inside-view rationale (~20% for narrow scenario); I accepted this by lifting bin_1 to ~0.13 and slightly raising bin_0, reflecting the genuine ADI-split compression mechanism. The result is a flatter, more honest distribution centered on bin_3 but with broader shoulders — closer to the inside-view variant than the over-confident outside-view.
[ceiling] Bin_8 (Above 45) should be zero because the stated answer range is open upper at 45.0
[anchoring] Shift more mass into wide-margin bins (5–8) because MLSTP absence + 2016 analogue argues for ~25 pp+ margin
| Bin | Probability |
|---|---|
| 0-5.6 (bin_0) | 5.0% |
| 5.6-11.3 (bin_1) | 12.0% |
| 11.3-16.9 (bin_2) | 21.0% |
| 16.9-22.5 (bin_3) | 27.0% |
| 22.5-28.1 (bin_4) | 16.0% |
| 28.1-33.8 (bin_5) | 10.0% |
| 33.8-39.4 (bin_6) | 5.0% |
| 39.4-45 (bin_7) | 3.0% |
| Above 45 (bin_8) | 1.0% |
wooley_rhino • run 5df63651 • $3.25 • 5m56s
Extracted Percentile Values: {0.1: 1.05, 1.0: 1.7, 5.0: 3.7, 10.0: 5.3, 15.0: 6.7, 20.0: 7.9, 25.0: 9.0, 30.0: 10.1, 35.0: 11.2, 40.0: 12.3, 45.0: 13.3, 46.0: 13.5, 47.0: 13.8, 48.0: 14.1, 49.0: 14.4, 50.0: 14.7, 51.0: 15.0, 52.0: 15.3, 53.0: 15.6, 54.0: 15.9, 55.0: 16.2, 60.0: 17.6, 65.0: 19.2, 70.0: 21.0, 75.0: 23.1, 80.0: 25.7, 85.0: 28.8, 90.0: 32.5, 95.0: 36.8, 99.0: 42.8, 99.9: 47.2}
Model’s Answer: Step one is setting the base rate. The best hard evidence is the historical first-round gap between first and second in São Tomé e Príncipe presidential elections. The recent pattern is roughly mid-teens to mid-twenties percentage points, with 2021 especially relevant because it was also a crowded field and produced a gap around the high teens. On history alone, I would start near about 18 to 19 points.
Step two is adjusting for the live 2026 context, which matters more than the old average. The strongest recent signals are that the field appears very fragmented again, that there are many would-be candidates, and that there are signs of tension within the ADI camp rather than perfect consolidation behind one official ruling-party vehicle. An incumbent, Carlos Vila Nova, is still likely to be the best-known and structurally strongest candidate, but a split or semi-split on his side makes a lower first-round lead more plausible than the raw historical median would suggest. That pulls me down from the historical high-teens center toward the mid-teens.
Step three is thinking through likely electoral geometry. In a small, personalist democracy with weak polling and many candidacies, the most common shape is not a razor-thin two-candidate duel and not a landslide, but a leading candidate in roughly the upper 20s to upper 30s and a runner-up in the mid-teens to low 20s. That naturally produces a margin around about 10 to 20 points. Given the time remaining is short, really large opinion shifts are less likely than alliance clarifications, withdrawals, or ballot-qualification changes. So the distribution should be centered fairly tightly inside that band, but still with meaningful tails because the candidate field is uncertain.
The background-source weighting I’m using is: historical election results are the most reliable anchor for the exact metric; recent reporting on candidacies and ADI tensions is the most important directional update; Wikipedia-style aggregation is useful but lower-confidence than major media or official filings; and the absence of polling means I should stay humble and widen the distribution.
My biggest swing assumptions are these. First, I am assuming Vila Nova is indeed the clear frontrunner, even if not fully backed by a united ADI. I’d put about a 25% chance that this is materially wrong; if so, the race becomes more open and the margin could compress sharply. Second, I am assuming the opposition remains fragmented rather than coalescing behind one main challenger. I’d put about a 35% chance this is wrong; if a single challenger consolidates anti-incumbent votes, the margin shifts down, potentially into single digits. Third, I am assuming the ADI split is real but limited, not a full implosion. I’d put about a 30% chance that this is wrong in either direction; a deeper split lowers the lead, while late reunification raises it.
A low outcome would come from late consolidation: several candidates withdraw or fade, one main challenger becomes the anti-incumbent focal point, and Vila Nova’s side leaks votes to another ADI-linked candidate. Then the top two could both land in the 20s or low 30s and the lead could be only a few points. I think the chance of a genuinely low result, roughly 8 points or less, is noticeable but still a minority outcome.
A high outcome would come from the incumbent retaining broad personal legitimacy while opponents fragment badly. In that world, Vila Nova could reach the high 30s or low 40s while the runner-up stays in the mid-teens, giving a lead in the 20s or low 30s. I think that is less likely than the middle case but still quite plausible. A truly extreme result above 45 points would require near-total opposition fragmentation plus an outright or near-outright first-round dominance, which is very unlikely but not impossible, so I leave only a tiny tail there.
My overall median is therefore in the mid-teens, below the historical central tendency but not dramatically so. The short horizon favors the structural base case; the fragmented field and intraparty tension shift the center downward; and the lack of polling means the interval should stay broad.
Percentile .1: 1.05 Percentile 1: 1.7 Percentile 5: 3.7 Percentile 10: 5.3 Percentile 15: 6.7 Percentile 20: 7.9 Percentile 25: 9.0 Percentile 30: 10.1 Percentile 35: 11.2 Percentile 40: 12.3 Percentile 45: 13.3 Percentile 46: 13.5 Percentile 47: 13.8 Percentile 48: 14.1 Percentile 49: 14.4 Percentile 50: 14.7 Percentile 51: 15.0 Percentile 52: 15.3 Percentile 53: 15.6 Percentile 54: 15.9 Percentile 55: 16.2 Percentile 60: 17.6 Percentile 65: 19.2 Percentile 70: 21.0 Percentile 75: 23.1 Percentile 80: 25.7 Percentile 85: 28.8 Percentile 90: 32.5 Percentile 95: 36.8 Percentile 99: 42.8 Percentile 99.9: 47.2
The two-round electoral rule and a small, concentrated electorate favor early vote consolidation by prominent figures.
Past contested first rounds typically produced clear first-place margins, creating a strong structural baseline for a sizable lead.
Incumbent-aligned networks, cross-party endorsements, and MDFM/UL’s move toward the incumbent concentrate votes on familiar names.
The ADI leadership split and the apparent absence of a unified MLSTP ticket are the immediate pressures pulling the margin toward the mid-teens.
If Nito consolidates ADI’s organization and Trovoada-aligned supporters coalesce, the margin will compress toward single digits.
If MLSTP stands aside or minor parties consolidate behind Vila Nova, the margin will widen into the high teens or low twenties.
Unresolved legal admissibility rulings, unpaid campaign fines, and late endorsements are the primary uncertainties that can reallocate decisive vote shares.
Certification timing, diaspora counting, and the inherent volatility of a small electorate leave a nontrivial tail of outcomes both below and above the mid-teens estimate.
Forecast: median = 18.1646 percentage points
By how many percentage points will the first-place candidate lead the second-place candidate in the first round of São Tomé e Príncipe’s July 19, 2026 presidential election?
Key figures
Historical context
São Tomé e Príncipe is a stable semi-presidential democracy with a history of competitive elections. Historically, first-round presidential margins have shown significant variance:
Tailwinds
Headwinds
Detailed reasoning
My forecast is built upon a synthesis of historical performance and a specific ‘inside view’ of the 2026 political landscape. Historically, São Tomé e Príncipe has produced a wide range of first-round margins, from a narrow 3.3 pp in 1996 to a high of 25.05 pp in 2016. The historical mean sits at 15.9 pp. However, simple historical averaging is insufficient for 2026 due to the unprecedented fragmentation of the dominant political force, the Independent Democratic Action (ADI) party.
In my reasoning, I heavily weighted the ADI split. The party, which won an absolute majority in the 2022 legislative elections (46.8%), is currently divided into two warring factions. One faction supports the incumbent President Carlos Vila Nova, while the leadership under Patrice Trovoada has endorsed parliamentary leader Nito Viegas d’Abreu. In a small electorate where the ADI usually serves as the primary engine for the frontrunner’s vote share, this split is highly likely to divide the ‘governing’ vote. If Vila Nova and d’Abreu both perform strongly, they may end up as the top two candidates with a very narrow gap between them, or one may fall to third place behind the opposition MLSTP-PSD candidate, Guilherme Posser da Costa. This fragmentation points toward a margin significantly lower than the 22.6 pp seen in 2021.
I also considered the administrative ‘funnel’ created by the Tribunal Constitucional (TC). The imposition of a 15,000 euro fine on 2021 candidates for campaign finance failures has, as of late May 2026, left only Carlos Vila Nova in full compliance among returning contenders. While this could theoretically lead to a landslide if rivals are disqualified, it is more likely to result in a consolidated field where the remaining major candidates (who have the resources to settle such fines or are new to the race) compete more fiercely for a smaller pool of ‘votos válidos.’
The resulting forecast uses a mixture model to account for these scenarios. I assigned the highest weight (approximately 45-50%) to a ‘fragmented race’ scenario where the top two candidates are separated by 8-12 pp. I balanced this with a ‘historical typical’ scenario (approx. 35%) where one candidate manages to consolidate enough support to lead by 15-18 pp, and a smaller probability (15%) of a near-tie (under 5 pp) if the ADI split is perfectly symmetrical. The most likely value of 9.68 pp reflects this expected compression of the margin due to intra-party competition.
Key uncertainties
Conclusion