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Direct measurement, that is without
statistical analysis, is preferable when possible. We have tried a
variety of simpler strategies in a diverse array of national surveys,
but none seem to do remotely as well as anchoring vignettes. For
example, we tried asking which of a set of vignettes the respondent is
most like, but we found that respondents had a difficult time
remembering them all at the same time. Another possibility is to ask
if the respondent has a higher or lower level of health/efficacy/etc
than the first vignette, and then the second, etc. This is better,
but it also does not fully correct for DIF in our experience, and in
any event would require assuming that DIF is fully corrected rather
than allowing empirical verification.
Another possibility of course is the usual strategy of trying to make
the self-assessment question even more concrete. This is always a
good strategy, but no matter how obvious and unambiguous a survey
question appears to the researcher, respondents always seem to
surprise us in their ability to interpret questions in different ways
than intended. This surprise of course is not revealed unless
researchers debrief respondents in post-interview debriefing sessions.
Researchers who are sure that their survey questions have no DIF need
to verify this at first with these interviews, but ideally also with
at least pretesting with anchoring vignettes.
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Gary King
2006-01-03