In Saturday’s Republican elections, Ted Cruz outperformed his pre-election polls in all three states where data was available: Kentucky, Louisiana, and Kansas. This is in contrast with Donald Trump, who performed within 1-2 percentage points in Kentucky and Louisiana…but underperformed by a remarkable 12 percentage points in Kansas. What’s going on?
Looking at the graph above, Cruz has always outperformed his polls – in 17 out of 18 states so far. The higher he is positioned in polls, the bigger the effect – and this weekend’s states were good ones for him to begin with. Overall, his eventual vote share is typically 1.3 times higher than his pre-election polls. That is a considerable difference.
It has been said that Cruz benefits from caucuses and closed elections in which independents cannot vote. However, when these features are present, he also runs stronger in polls. Overall we have three correlated variables – Cruz support, closed primaries, and caucuses – and so it is hard to say what is causative. The tendency for pollsters to undercount his supporters may affect estimates of what will happen in elections from now to March 15th, most of which are closed and/or caucuses.