Factor mixture modeling was used to investigate potential response incongruity between positively and negatively worded items. Survey respondents (N = 591) answered questions about job satisfaction and dissatisfaction. Results revealed two classes of respondent: a majority class, who generally do not have problems answering positively and negatively worded items, and a minority class, who have serious trouble with negatively worded items. With the exclusion of the minority class, job satisfaction and dissatisfaction were found to be essentially unidimensional rather than bidimensional as previous research had suggested. These results challenge previous findings regarding the bidimensionality of job satisfaction and cast doubt on the widespread research practice of assuming population homogeneity in survey responses. A detailed flowchart illustrating the analytic procedure and an Mplus syntax program are provided so that researchers can conduct similar investigations on constructs of interest.