Although the use of Cognitive Interviewing (CI) has become a common practice in survey research, there is a still pervasive doubt about if CI detects "real problems", and is really helpful in investigating what the survey questions are truly measuring. The lack of confidence can be partially due to the absence of methodological link between qualitative evidence provided by CI and quantitative results from field tests. The rationale behind our proposal is to restore to mixed methods research to investigate whether CI findings can contribute to improve validity of survey estimates. We illustrate how a mixed method approach that incorporates CI with quantitative methods can begin to address this problem. This paper comes out of a larger study to evaluate a set of disability questions for comparability across the US and six Asian countries. For this paper, we draw on data collected in the US, and we will focus our analysis on the particular disability questions intended to measure "pain". 40 interviews conducted in the US to identify interpretive patterns, calculations processes, and types of response error problems. Based on the analysis of those interviews, follow-up probe questions were developed and placed on a field test questionnaire included in the 2010 National Health Interview Survey. Then, a multivariate logistic regression analyses were conducted to evaluate the performance of the "pain" question, and the follow-up probe questions. The benefits of a mixed methods approach to find out the extent to which CI findings can improve survey estimates will be...