This dissertation investigates the question: are mission critical occupations more favored than other occupations in performance appraisals in pay pools? While many types of bias in performance appraisals occur, such as gender or race, occupational bias--favoring or showing preference for one occupation over another in performance appraisals and subsequent ratings-- has not been fully examined. There is a lack of empirical evidence that addresses occupational bias in performance appraisal and ratings in the Federal civil service sector, and more specifically the Department of Defense. The importance of occupational bias in performance appraisals is seen in the cost to organization and taxpayer, the degradation to fairness and trust in the workplace, and the erosion of organizational values. The methodology used to address this dissertation's hypothesis is a quantitative-qualitative inquiry that investigates performance ratings of the engineering occupational series within three Department of Defense (DOD) engineering agencies. The methodology is comprised of three parts: quantitative analysis of pay pool rating data and qualitative analysis of archived documents and expert interviews. Each part of the methodology is intended to be mutually supportive. The quantitative analysis yields a null finding of the hypothesis based on two findings. First, indicators of occupational bias were not found using differences of average occupational performance ratings between engineers and other occupations in three DOD engineering organizations. Second, Fiscal Year 2008 engineer occupational series performance ratings in three Department of Defense engineering agencies did not show statistically significant differences when compared to occupations such as personnel management specialists and accountants. This may be due to privacy act limitations in the data set used. Anecdotal evidence of preferences for mission critical occupations in performance appraisals and ratings was found to support the hypothesis. / Ph. D.