Methodology

Overview

This tracker produces a daily weighted polling average of Swedish voting intention. It is not a prediction. It is an estimate of where public opinion currently stands, based on the best available polling data.

The model ingests polls from — pollsters, with the most recent poll conducted on —. The database currently contains — individual polls.

The tracker estimates support for eight parties: Socialdemokraterna (S), Sverigedemokraterna (SD), Moderaterna (M), Vänsterpartiet (V), Miljöpartiet de gröna (MP), Centerpartiet (C), Kristdemokraterna (KD), and Liberalerna (L), plus an "Others" category for smaller parties below the 4% electoral threshold.

What the model does

For each day, the model considers all published Swedish voting intention polls, weighting each by how recently it was conducted. Each poll receives a composite weight based on two factors: how recent it is and how large its sample was. The model then computes a weighted average for each party.

This approach is sometimes called a "poll of polls" or polling aggregate. It is designed to smooth out the noise from individual polls while still responding to genuine shifts in opinion.

The model reflects the polls. If polls are systematically biased, the model will reflect that bias. We do not apply ad-hoc corrections for past biases, because the direction and magnitude of polling error is unknown in advance. The model aggregates what pollsters report; it does not second-guess them.

Weighting factors

1. Recency

Polls are weighted by how recently their fieldwork was conducted, using exponential decay with a 14-day half-life. This means a poll conducted 14 days ago receives half the weight of a poll conducted today. There is no hard cutoff — the exponential decay ensures old polls contribute negligibly (a 60-day-old poll has just 4% of a fresh poll's weight).

Formula: w_recency = exp(−ln(2) × days_ago / 14)

2. Sample size

Larger polls receive more weight, since they provide more precise estimates. The weight is proportional to the square root of the sample size, normalised to a reference poll of 1,000 respondents. This is capped at 3× to prevent very large polls from dominating the average.

Formula: w_sample = min(√(n / 1000), 3.0)

Final weight

The final weight for each poll is the product of recency and sample size: recency × sample size. All Swedish pollsters are treated equally in the current version (v1.0). Future versions may introduce pollster reliability weighting as data accumulates.

Uncertainty bands

The tracker displays 90% uncertainty bands around each party estimate. These are calculated as the weighted standard deviation of polls in the recency window, multiplied by 1.645 (the z-score for a 90% interval). We call these "uncertainty bands" rather than "credible intervals" because the model is not fully Bayesian — these bands reflect pollster disagreement, not a formal posterior distribution.

Wide bands mean pollsters disagree significantly. Narrow bands mean there is strong consensus. A minimum band of ±2.0 percentage points is applied to every estimate, because even when pollsters agree, there is always some irreducible uncertainty in measuring public opinion.

Seat projection methodology

The Sainte-Laguë method

The tracker projects seat allocations using the modified Sainte-Laguë method, which is used in actual Swedish elections. Under this method, each party's vote share is divided by successive odd numbers (1, 3, 5, 7, ...) to produce a series of quotas. The 349 Riksdag seats are allocated to the highest quotas in order until all seats are distributed.

The 4% threshold

Sweden applies a 4% national electoral threshold. Parties polling below 4% receive zero seats, and their votes are redistributed among parties above the threshold using the Sainte-Laguë algorithm. This reflects the real Swedish electoral rule and helps clarify which parties would actually enter the parliament.

What the projections show

The model projects seats for the eight tracked parties and reports changes relative to the 2022 election result. A party needs 175 seats for a single-party majority in the 349-seat Riksdag. The projection also reports seat totals for three bloc groupings: the Left bloc (S + V + MP), the Right bloc (M + SD + KD + L), and Centre (C).

Coalition analysis

The three blocs

Swedish politics organises around three distinct blocs. The Left bloc comprises the Social Democrats, the Left Party, and the Greens. The Right bloc comprises the Moderates, the Sweden Democrats, the Christian Democrats, and the Liberals. The Centre Party stands alone.

Why Centre is king

The Centre Party holds a kingmaker role in Swedish politics. Since the 2022 election, it has cooperated with the left on key votes, despite its centre-right positioning. Critically, Centre refuses to govern in any coalition that includes the Sweden Democrats. This constraint makes the simple arithmetic of "Right bloc + Centre vs. Left bloc + Centre" insufficient — not all mathematically viable coalitions are politically viable.

What coalitions are possible

Left bloc alone or Left bloc + Centre are potential governments if they reach 175 seats. Right bloc alone is a potential government if it reaches 175 seats without SD (since Centre refuses to govern with SD). Right bloc + Centre is not viable because Centre will not work with SD. The tracker reports these combinations to help clarify the political landscape.

Data sources

Polling data is sourced from Swedish Wikipedia's polling tables, which aggregate polls published by Swedish polling institutes. Each poll entry includes pollster name, client, fieldwork dates, sample size, and party vote share figures. The Wikipedia tables serve as a publicly maintained record of Swedish electoral polling.

All entries include source attribution. Polls that fail validation checks are flagged and excluded from the model.

Known limitations

All polling aggregates have limitations. The key ones for this model are:

• •It relies on publicly published polls. Polls that are not published or are embargoed will not appear in the aggregate.
• •The current version treats all pollsters equally. As the dataset grows, future versions may introduce pollster reliability weighting.
• •The model treats all polls as measuring the same thing, even though question wording, weighting methods, and turnout assumptions differ between pollsters.
• •Seat projections use uniform national swing and do not account for regional variation or local electoral dynamics.
• •Coalition analysis is based on stated positions and historical patterns, not binding agreements. Political negotiations can produce surprising outcomes.

Version history

v1.0 (March 2026) — Initial release. Weighted rolling average with recency decay (14-day half-life), sample-size weighting (square root, normalised to 1000, capped at 3×), and equal treatment of all Swedish pollsters. Eight parties tracked: S, SD, M, V, MP, C, KD, L (plus Others). 90% uncertainty bands with 2.0pp minimum. Seat projection using modified Sainte-Laguë method with 4% electoral threshold (349 seats, 175 needed for majority). Coalition analysis with Left bloc (S+V+MP), Right bloc (M+SD+KD+L), and Centre party kingmaker role. Data sourced from Swedish Wikipedia polling tables.