On average, about half the respondents to surveys do not answer one or more questions analyzed in the average survey-based political science article. Almost all analysts contaminate their data at least partially by filling in educated guesses for some of these items (such as coding "don't know" on party identification questions as "independent"). Our review of a large part of the recent literature suggests that approximately 94% use listwise deletion to eliminate entire observations (losing about one-third of their data, on average) when any one variable remains missing after filling in guesses for some.(1) Of course, similar problems with missing data occur in nonsurvey ...