liesdamned liesand statistics sampling bias during world war iiwhenever an allied plane would return from mission over europe the plane would be inspected to see where the flak had impacted based upon this datamechanics reinforced those areas of the planes that seemed most likely to be hit by flak what' wrong with thisthey did not inspect the planes that failed to return from missions because they had been downed by flak perhaps these unexamined planes failed to return precisely because they were hit in the places where the flak would do the most damage this particular error is called nonresponse bias it is quite common in surveys at many universitiesfor examplesstudents are asked during one of the lectures late in the term to fill out form rating the quality of the professor' lectures though the results of such surveys are often unflatteringthey could be worse those students who think that the lectures are so bad that they aren' worth attending are not included in the survey as we said earlierall statistical techniques are based upon the assumption that by sampling subset of population we can infer things about the population as whole if random sampling is usedwe can make precise mathematical statements about the expected relationship of the sample to the entire population unfortunatelymany studiesparticularly in the social sciencesare based on what has been called convenience (or accidentalsampling this involves choosing samples based on how easy they are to procure why do so many psychological studies use populations of undergraduatesbecause they are easy to find on college campuses convenience sample might be representativebut there is no way of knowing whether it actually is representative the family research institute' web site contains table with the following informationtable how long do homosexuals live the move to online surveyswhich allows students who do not attend class to participate in the surveydoes not augur well for the egos of professors