The use of control variables is widespread in [international] entrepreneurship research. Herman Aguinis notes there are many  judgment calls, undisclosed practices, and an overall lack of transparency in what controls are included and excluded, and how their usage is reported. He also suggests these practices may partially account for a lack of repeatability of empirical results.

To help address concerns about control variable usage, he has made the following article available at http://mypage.iu.edu/~haguinis/pubs.html (item #126):

Bernerth, J. & Aguinis, H. 2016. A critical review and best-practice recommendations for control variable usage. Personnel Psychology, 69: 229-283.

You may also be interested in reviewing other methods paper in Herman’s list.