Ignacio Lago, "Rational Expectations or Heuristics? Strategic Voting in Proportional Representation Systems," Party Politics, 14 (January, 2008), 31-49.

First paragraph:
In this article, I critically review the impact of district magnitude on strategic voting as stated in Duvergerian or electoral coordination theories: in proportional representation (PR) systems with large districts (i.e. greater than five seats), strategic voting is not possible because voters do not have good enough expectations about how well each party or candidate is likely to do in the upcoming election (Cox, 1997; Cox and Shugart, 1996). I argue that the necessary informational requirements for voting strategically in large districts are surprisingly low. Voters only need to know whether the party they prefer has some chance of winning at least one seat in their district. Given that they have too small a stake in elections to collect information, voters may muddle through, however, relying on a shortcut such as the electoral history heuristic (i.e. expectations about the likely outcome of the election grounded in simple extrapolations from the previous one). The heuristic voters employ in t is simply the viability of their preferred party in their district in the previous election or, in other words, whether their preferred party gained at least one seat in their district in t-1. When electoral expectations are formed in accordance with this shortcut, strategic voting can also be possible in large districts, since this information is as cheap to come by there as in less than five-seat districts.

Figures and Tables:

Table 1. Electoral results in the Spanish elections of the PCE/IU

Table 2. Knowledge of district magnitude in Spain, 2004

Table 3. Knowledge of district magnitude in Spain, 2004, with an error of ±1 seat

Table 4. Has the IU gained seats in your district (Spain, 2004)?

Table 5. Binomial logit estimates, 1979 election

Table 6. Binomial logit estimates, 1982 election

Table 7. Predicted strategic and sincere votes according to rational expectations, 1979 election

Table 8. Predicted strategic and sincere votes according to heuristics, 1979 election

Table 9. Predicted strategic and sincere votes according to heuristics, 1982 election

Appendix: Variables in the Analysis of the 1979 and 1982 elections

First paragraph of Conclusion:
In this article, I have demonstrated that strategic voting in PR systems does not depend on rational expectations, but on heuristics. In order to form electoral expectations, voters can employ the electoral history heuristic (i.e. the viability of their preferred party in their district in the previous election). First, I have shown that very few people in the 2004 Spanish election knew how many seats were elected in their districts. On the contrary, the vast majority knew the focal point that solves coordination problems in mass elections: whether (minor) parties have previously gained at least one seat in a given district. Second, these two approaches were applied to the analysis of the 1979 and 1982 elections in Spain. Both found a significant extent of strategic voting in the 1979 election: according to the model based on rational expectations, 4.6 percent of PCE sympathizers cast a strategic vote, while for the explanation that relies on heuristics this percentage is 8.9. But the divergence is particularly important in the 1982 election. When electoral coordination depends on rational expectations, there is no evidence of strategic voting. However, when it is a function of heuristics, 8.5 percent of PCE supporters voted strategically. The main conclusion from this research is that strategic voting is observable across all districts, and not just in small ones.