There is an excellent essay on Charles Franklin’s blog, Political Arithmetik, on the Palestinian exit polls. Charles is a leading expert on polling and statistics, and his blog is worth reading just to see what is currently on his mind.
But in his February 22 entry, “WSJ Numbers Guy on Palestinian Exit Polls”, Charles digs a bit into the issue of polling errors in exit poll data. The issue at hand, just as was the case regarding the 2004 presidential election exit polls in the United States, is how can we know that survey response errors (in the case of the 2004 U.S. election and in the recent Palestinian election) are more likely to come from one political party relative to others. Here’s what Charles wrote:
But here is the rub: How do you know the non-responses are overwhelmingly for Hamas? (Or for George Bush in 2004?) There may be good reason to think this is so, but what data support the inference? In the U.S. we have the advantage of sample precinct returns which provide a check on the exit polls. As data come in from sample precincts they are compared with exit results from the same precinct, which allows estimation of how much non-response might be affecting the exit results. Such an option doesn’t exist in the Palestinian case, where the counting process is much slower. So a Palestinian exit pollster is faced with a dilemma: adjust the results based on substantive expectations (really, your best subjective judgement about non-respondents) and admit that your statistical results are shifted by a clearly non-data driven component (which could be wrong). OR, decline to introduce non-data driven elements into the calculations, with the clear risk that your results may be biased by selective non-response. That is a really tough decision. (A third option would be to compare current results with historical election returns, but in the Palestinian case there is very little past election data to use. That will, of course, improve over time if democratic elections continue to be the practice. Such a comparison can’t account for across the board shifts, but might provide some leverage on non-response that is otherwise unavailable.)
Charles then notes that he is going to dig into this in more detail in the future, and gives links to two websites with data on the exit polls in the Palestinian elections: the Palestinian Center for Policy and Survey Research (PCPSR) and the Development Studies Programme of Birzeit University (DSP).
I’ll keep watching Charles’ blog for updates, but Election Updates readers might want to bookmark his blog for themselves!