EXPRESS: Response Aggregation to Obtain Truthful Answers to Sensitive Questions: Estimating the Prevalence of Illegal Purchases of Prescription Drugs

We propose a simple, new technique to obtain truthful answers to sensitive, categorical questions. The Paired Response Technique (PRT) asks participants to merely report the sum of the answers to two paired questions, one baseline and one sensitive, with the answers to each separate question only known to the participants. The technique then statistically infers the prevalence of the sensitive characteristic and its potential drivers from the association of the baseline question with other questions in the survey. Monte Carlo simulations demonstrate the performance of the PRT under varying conditions. A representative survey (n = 4,649) in the Netherlands about legal and illegal purchases of prescription drugs to enhance sexual performance reveals that 17.4 % of the target population has purchased at least once medication to enhance sexual performance. In contrast, in a control group surveyed with direct questioning, only 5.1 % admit having done so. The great majority of these individuals opt to purchase illegally. Two further empirical applications, respectively, in the U.S. and in the U.K., show that the PRT reduces cognitive and affective costs of survey participation compared to a state-of-the-art Randomized Response Technique for categorical questions.