A few weeks ago, Bryan Caplan pointed out this great working paper by David Hedengren and Thomas Stratmann:

**The Dog that Didn't Bark: What Item Non-Response Shows about Cognitive and ****Non-Cognitive Ability **

What survey respondents choose not to answer (item non-response) provides a useful task based measure of cognitive ability (e.g., IQ) and non-cognitive ability (e.g., Conscientiousness). Using the German Socio-Economic Panel (SOEP) and the National Longitudinal Survey of Youth 1997 (NLSY97), we find consistent correlation between item non-response and traditional measures of IQ and Conscientiousness. We also find that item non-response is more strongly correlated with earnings in the SOEP than traditional measures of either IQ or Conscientiousness. We also use the Survey of Income and Program Participation (SIPP) Gold Standard, which has no explicit measure of either cognitive or non-cognitive ability, to show that item non-response predicts earnings from self-reported and administrative sources. Consistent with previous work showing that Conscientiousness and IQ are positively associated with longevity, we document that item non-response is associated with decreased mortality risk. Our findings suggest that item non-response provides an important measure of cognitive and non-cognitive ability that is contained on every survey.

The triumph of this paper is the mass of survey data to which this technique can be applied. As the authors state in the opening paragraph:

Studying the importance of non-cognitive skills, such as conscientiousness, perseverance, and motivation, has been hamstrung by the fact that many popular data sets in economics do not contain information on an individual's personality traits. However, surveys contain a valuable but neglected piece of data: what respondents do not say. Respondents skip, refuse to answer, or claim ignorance on at least a few questions in virtually all surveys. When a respondent forgets to fill in answers to some questions on the survey form, or refuses to provide an answer to the interviewer, we gain important information about the respondent.