Index Framework
The mathematical definitions of every index used across EZstates Elections — P, CP, SP, V, and the Key–Campbell classification scalar W(t).
P Partisanship Index
Where D = % of group voting Democratic, R = % voting Republican. Ranges from −1 (fully Republican) to +1 (fully Democratic). Zero means the group is evenly split.
- P > 0 — group leans Democratic
- P < 0 — group leans Republican
- |P| > 0.4 — strongly partisan (reliable base)
- |P| < 0.1 — centrist (persuasion target)
CP Critical Power (Partisan Power)
Measures how much a group contributes to the stable partisan margin of an election. A group must be both large and strongly partisan to score high. Groups with high CP anchor a candidate's base — the strategic imperative is mobilization.
- group_share — fraction of the electorate (0–1)
- |P| — absolute partisan lean
SP Swing Power (Volatility Power)
Measures how much a group contributes to election-to-election volatility. A group must be both large and volatile across cycles to score high. Groups with high SP decide close elections — the strategic imperative is persuasion.
- group_share — fraction of the electorate (0–1)
- V_total — combined volatility score (see below)
V Volatility Indices
Three complementary volatility measures computed across the full group × state × year dataset:
- V_time — how much a group's P fluctuates across election years (temporal instability)
- V_space — how much a group's P varies across states in the same year (geographic dispersion)
- V_total — Euclidean combination; the primary volatility signal used in SP
W(t) — Key–Campbell Election Classification
A CP-weighted mean of absolute partisan shift across all groups between election t−1 and t. Higher W(t) = more coalition movement = more transformative election.
- ΔP_g(t) = P_g(t) − P_g(t−1) for group g
- CP_g(t) = weight (larger, more partisan groups count more)
| W(t) Range | Election Type | Interpretation |
|---|---|---|
| W < 0.04 | Maintaining | Normal vote holds; no significant coalition movement |
| 0.04 ≤ W < 0.08 | Deviating | Temporary shift; existing alignment largely intact |
| 0.08 ≤ W < 0.14 | Converting | Substantial realignment of key groups |
| W ≥ 0.14 | Realigning | Deep, durable shift in partisan coalition structure |
cand_won_due_to_group — Binary Decisive Test
A switcher group is flagged as individually decisive when the candidate's margin of victory in the state is smaller than the estimated Democratic vote gain attributable to that group's switch. In other words: without this group's switch, the candidate would have lost the state.
Actual distribution of each index across all group × state observations for the selected year. Auto-updates when new election data is added. Use these figures to contextualise any individual value you see elsewhere in the system.