Your article on ecological inference brought to mind another interesting technique for predicting election results: stock markets (This Week, 26 April, p 5).
The University of Iowa has run a presidential election "stock market" since at least 1991. Its participants trade contracts (Democrat, Republican) whose final value is equal to the percentage of the popular vote obtained by that party's candidate. It is therefore in the traders' interests to make use of as much information as possible, including that generated from opinion polls. Consequently the stock market consistently outperforms polls.
Further, with prices changing constantly, new information is constantly being reflected in the market, providing an up-to-date prediction all of the time.
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