Association for Public Policy Analysis & Management

The increasing reliance on adjunct instructors has been a remarkable trend in higher education for the past few decades. According to a recent NCES report, the proportion of part-time faculty in postsecondary institutions has increased from 20% in 1971 to nearly 50% in 2009. Such increase has been particularly pronounced in two-year public institutions, where  more than 70% of faculty are adjuncts in 2009. Many studies have explored the potential impacts of adjuncts on student learning outcomes. Yet, most of them are conducted in four-year institutions with sharply divided findings and conclusions. Opposing arguments about the relative advantages and disadvantages of adjuncts, as well as the mixed findings from empirical research have led policymakers and researchers to a growing awareness that the impact of adjuncts may be both heterogeneous and multifaceted, and may largely depend on the setting of the study, the specific characteristics of the instructor, the discipline of instruction, and the particular student outcome measured.

Using a unique administrative data set on both public two-year and four-year institutions in an entire state, this paper contributes to the teacher effectiveness literature in three major ways: 1) we compared the characteristics and impacts of adjunct instructors in two-year versus four year institutions; 2) taking advantage of the detailed instructor characteristics (demographic information, academic rank, degree attainment, and time distribution across different activities and institutions), we not only estimated the potential heterogeneity in the impacts of adjuncts by instructor profiles and disciplines of study, but also explored the potential mechanisms through which adjuncts influences student outcomes ; 3) this is the first study to examine the impacts of adjuncts on student labor market performance. To address student sorting by the type of instructor, we followed Bettinger & Long (2010)’s work on employing an instrumental variable strategy , where we used the term-by-term variation in departmental faculty composition as an instrument for  the student’s likelihood of taking a particular course with an adjunct instructor.