Do tenured and tenure-track faculty matter?

"During the last two decades, there has been a significant growth in the share of faculty members at American colleges and universities that are employed in part-time or in full-time non tenure-track positions. Our study is the first to address whether the increased usage of such faculty adversely affects undergraduate students' graduation rates. Using institutional level panel data from the College Board and other sources, our econometric analyses suggest that the increased usage of these faculty types does adversely affect graduation rates of students at 4-year colleges, with the largest impact on students being felt at the public masters-level institutions"--National Bureau of Economic Research web site.