Researchers usually examine the quality of survey data by methods such as the test-retest reliability. However, those methods are mainly designed to examine the quality of an individual measurement, rather than the quality of a data set as a whole. There is a relative lack of methods for evaluation of the overall data quality. This paper attempts to fill this gap. We propose to use interviewers’ assessments as one of criteria for evaluating the overall data quality. Interviewers are the ones who literally conduct and thus directly observe interviews. Taiwan’s Election and Democratization Studies (TEDS) have required these front-line survey practitioners to assess how trustworthy the responses of each of their interviewees are, and to provide several descriptions about the process and environment of the conducted interview. We take this information into consideration to evaluate the data quality of TEDS surveys and compare it with the results from the conventional test-retest method to see whether or not interviewers’ assessment is informative in terms of data quality.