Quantitative Sozialforschung
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Privacy Concerns in Responses to Sensitive Questions

A Survey Experiment on the Influence of Numeric Codes on Unit Nonresponse, Item Nonresponse, and Misreporting

Felix Bader, Johannes Bauer, Martina Kroher, Patrick Riordan

Paper-and-pencil surveys are a widely used method for gaining data. Numeric codes printed on the questionnaire are often applied by scan software for a fast and efficient entering of the data. However printed numbers on a questionnaire can provoke concerns about anonymity that may lead to unit nonresponse, item nonresponse and misreporting.


For testing this, we conducted an experiment in a mail survey on group-focused enmity, printing a scanner code on half of the questionnaires. Our results show no significant deviation in case of unit nonresponse. We found an increase in nonresponse to sensitive items between questionnaires with and without codes. There is also a misreporting bias towards socially desirable answers to sensitive questions for questionnaires with a statement to the numeric code in the cover letter. Therefore one needs to trade off these small biases against the usefulness of the code. From a methodological perspective we recommend not to make a statement concerning the numeric code in the cover letter.
Our results are of relevance for researchers conducting paper-and-pencil surveys as well as for those analyzing data sets from these surveys. While this article analyses biases caused by scanner codes, it is also useful for scientists interested in imprinted identification numbers in order to utilize paradata.

Additional Information

Questionnaire and cover letter (in German)

questionnaire with numeric code (PDF, 97 KB)
cover letter, group without notice (PDF, 71 KB)
cover letter, group with notice (PDF, 71 KB)

Source code and data sets

source_code (rar, 13 KB)
data sets can be obtained upon request

Results of the GFE Study

report (in German)

Sampling methodology

presentation (in German, PDF 1.6 MB)