What are historical case studies where switching from D’Hondt to STV (or vice versa) changed party systems?
Executive summary
Several observable historical instances show that switching between D’Hondt (a party-list highest‑averages method) and Single Transferable Vote (STV, a candidate‑centred PR system) reshaped party incentives, fragmentation and intra‑party competition: notable examples include the UK’s shift to list‑PR (D’Hondt) for European elections in 1999 versus Northern Ireland’s persistent STV practice since 1979, the Australian Capital Territory’s pre‑1992 use of D’Hondt before adopting Hare‑Clark (an STV variant), and institutional uses of D’Hondt in Northern Ireland’s power‑sharing that alter coalition dynamics (sources: Constitution Unit, The National, Pelican Magazine, European Parliament briefing) [1] [2] [3] [4].
1. How the UK’s 1999 move to D’Hondt for European elections reshaped party payoffs
When Great Britain moved European Parliament elections from first‑past‑the‑post to a regional party‑list system using D’Hondt in 1999, the mechanics—regional lists allocated by D’Hondt—favoured larger parties within small regions and reduced wasted majority effects compared to FPTP, which changed incentives for small parties and strategic cooperation; commentators note that results under D’Hondt were “proportional, but not very” and that outcomes would have differed from the old FPTP arrangements [1] [5].
2. Northern Ireland’s long use of STV and the counterfactual contrast
Northern Ireland has used STV for European elections since 1979, and reporting repeatedly highlights STV’s candidate focus and closer proportionality—voters rank individuals and can, for example, support candidates of a single gender across parties—producing different electoral and party incentives than list‑D’Hondt systems where voters choose parties rather than individuals [1] [2]. This sustained STV practice is a useful comparator to show how STV tends to encourage local candidate competition and reduce party‑list control over selection [2].
3. The Australian Capital Territory: a practical switch from D’Hondt to STV (Hare‑Clark)
Electoral analysts record that the Australian Capital Territory once used a D’Hondt‑style allocation before switching to the Hare‑Clark STV system in 1992, and that Australia more broadly favors STV models; while the sources do not quantify the exact party‑system consequences, the switch is presented as emblematic of a move from party‑list dominance toward candidate‑centred proportionality that typically increases intra‑party competition and can alter the fortunes of smaller parties and independents [3].
4. D’Hondt in mixed systems and engineered moderation of fragmentation
Across Europe, D’Hondt is commonly used in party‑list contexts (e.g., Scotland’s regional AM allocation, Spain, Belgium) and is analytically associated with favoring larger parties and reducing fragmentation relative to other proportional formulas—academic summaries and briefings stress that D’Hondt “favors larger parties” and tends to reduce political fragmentation, an effect that shapes party strategies and coalition arithmetic where it is introduced [6] [7] [4]. The practical effect: switching toward D’Hondt often nudges systems to fewer medium‑sized parties; switching away can open space for smaller parties.
5. Institutional uses of D’Hondt that change party behaviour without a formal electoral redesign
Northern Ireland’s use of D’Hondt for ministerial allocation under the Good Friday arrangements is a salient non‑electoral example: using D’Hondt to allocate posts forces power‑sharing and gives the largest unionist and republican parties guaranteed posts, thereby producing “forced coalitions” and institutional incentives distinct from pure STV electoral outcomes—which in turn affects party bargaining and campaign strategies [3].
6. Limits of the evidence and competing viewpoints
Sources converge that D’Hondt mechanically advantages larger lists and that STV emphasizes individual candidate choice and closer proportionality [6] [2], but granular causal claims—exact seat swings or long‑run party realignment after a switch—require case‑by‑case empirical studies not present in the supplied reporting; some commentators argue D’Hondt’s “moderating” effect aids governability while critics say it preserves dominance of established parties [6] [8]. Taken together, the clearest historical lessons in the supplied material are directional: switching to D’Hondt tends to consolidate party systems modestly; switching to STV tends to empower individual candidates, small parties and independents [1] [2] [3].