“Nate M. Jensen”:http://pages.wustl.edu/nathanjensen/articles/1763 provides a nice overview of corruption, and the difficulties of getting straight answers on sensitive questions in survey research.
bq. Dan Treisman has an excellent Annual Review of Political Science piece reviewing the corruption literature and comparing the findings from studies using expert assessments versus individual experiences. … The provocative conjecture from Treisman is that perception based measures may suffer from serious bias. Experts believe that countries with democratic institutions, for example, are less corruption. Thus when asked of how corrupt country X is, they use the level of democracy to evaluate the level of corruption. The point is that democracy may not cause lower levels of corruption. Democracy causes people to think a country is less corrupt. Then we run regressions using this data and find that democracies are less corrupt … Due to these problems, many corruption researcher have begun to focus on asking individuals about their personal experiences with corruption. This is especially prevalent in firm level surveys of the business environment across countries. Without going into too many details, there are a few problems with this approach. In a paper with Quan Li and Aminur Rahman, we observe some weird patterns in cross-national business corruption data. Why does China and Kenya show up as having low levels of business corruption? Why is Germany so high? Our main finding is that there is systematic “non-response” bias. Lots of firms don’t answer these questions, and this number increases in countries with more authoritarian institutions and less press freedom. This non-response bias helps us explain these weird patterns.
bq. One response is to try to help shield respondents from any potential repercussions from answering honestly. One practical way to achieve this is to give respondents a coin and have them flip it without showing the enumerator. …First question, have you ever paid a bribe to a police officer? Flip the coin. If it lands heads, say yes no matter what. If it lands tails, answer honestly. … The logic behind this is: a) respondents have plausible deniability since they can always claim that they answered yes due flipping heads and b) laws of probability tells us that on average, each question should have at least 50% yes answers, and c) it if very unlikely that respondents would answer “no” seven times in a row (flipping 7 heads in a row). … In a survey of firms in Bangladesh, Aminur Rahman and I fielded corruption and tax questions to firms. The coin flip technique dictates that at least 50% of responses should be “yes”. For a bunch of the questions, such as cheating on taxes, we had responses well below 50%. This means, even with the deniability assured by the coin flip technique, the pattern of responses indicates systematic underreporting of tax evasion.