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Quorum — did enough of the electorate show up?

One line: quorum is a turnout threshold, separate from who wins: enough of the eligible electorate must participate for the election to count. It's opt-in (set eligible_voters and/or quorum), and a cast abstention counts toward it — showing up and turning in a blank ballot is still participation.

→ What an abstention is: GLOSSARY · the abstention vs Equal Support distinction: the abstention lesson · how results are reported: STAR Reporting.

How it works in the engine

Quorum is only checked when a file opts in. Two inputs:

  • eligible_voters — the size of the electorate (aliases: electorate, registered_voters). This is an external number; it is not in the ballots.
  • quorum — the threshold (alias: minimum_quorum):
  • omitted → default: a majority (>50%) of eligible voters;
  • a percentage ("50%", or 0.5) → that fraction of eligible voters;
  • an integer ≥ 1 → an absolute minimum number of ballots.

Participation = total ballots cast, abstentions included. If quorum is not met, the engine declares no winner (turnout failed), rather than crowning one on too few votes. A percentage/majority quorum needs eligible_voters; without it the engine says "quorum not assessed" rather than inventing a denominator.

Worked example — the abstention that carries quorum

A 10-member board; six submit a ballot, one of them blank. No explicit quorum, so the default is a majority of 10 — at least 6 (quorum_demo_c3_b6.yaml):

 Quorum: 6 of 10 eligible voters participated (60% turnout); requires more than 50% (>= 6). MET.
 Tabulating 6 ballots. Note: 1 of 6 ballots is marked as an abstention.
 ...
 Anna wins.
   Voters with a preference: 5 of 6 (1 Equal Support).
   Anna 3 (60%) vs Ben 2 (40%); majority = 3.

The blank ballot is the sixth participant. Because a cast abstention counts toward quorum, turnout reaches 6 and the election is valid — drop that abstention and quorum would fail (5 of 10). The abstainer changed no candidate's score, but their presence made the result count. Full report: quorum_demo_c3_b6_tabulated.txt.

Won the count, but not elected (quorum fails)

Take the exact same six ballots — Anna wins the tabulation — and change only the assumed electorate. For teaching, invent one: "the electorate is the turnout plus another 100%," so eligible_voters: 12 (quorum_fail_demo_c3_b6.yaml). (That "cast + X%" rule is a demo device only — real elections use the actual registered roll, never a formula off the ballots.)

--- STAR Voting Method (single winner) ---
 Quorum: 6 of 12 eligible voters participated (50% turnout); requires more than 50% (>= 7). NOT MET.
 No winner declared — quorum not reached.

Exactly half turned out, and a quorum is a strict majority, so 50% fails by one. Anna won the vote, but winning the vote and being elected are different things when turnout falls short — the engine stops before declaring a winner. (Note it bails before tabulating, so it doesn't reprint who would have won; that's the quorum-met run above, on the same ballots.)

Why eligible_voters isn't auto-filled from the ballots

It's tempting to default eligible_voters to the number of ballots cast — but that makes participation always equal eligibility, so turnout would always read 100% and quorum would always pass, defeating the entire check. A turnout quorum is meaningful only against the real electorate, which has to be supplied from outside the ballot data. So the engine keeps eligible_voters an explicit, optional input and stays silent when it's unknown. (For the same reason there's no "eligible = cast + X%" engine option — it would bake a fiction into the tool when you can already type a literal number for a demo, as the files above do.)

Quorum vs the runoff denominator — three different "how many"

Don't confuse these (they answer different questions):

Count Question it answers
Eligible voters how many could vote (the electorate) — the quorum denominator
Ballots cast (incl. abstentions) how many did participate — the quorum numerator
Voters with a preference of those, how many picked between the two finalists — the runoff percentage denominator

An abstention drops out of the runoff denominator (no preference) but stays in the quorum numerator (still participated). That's the whole reason the two counts can differ — see Equal Support vs abstention.