“…4 As pointed out by Cahuc (2018), the findings relying on firm data are still scarce and, until recently, did not establish a consensus about the effectiveness of STW programs. With the exception of Boeri and Bruecker (2011), most of these studies suggest small or even negative effects of STW on employment in different contexts (Calavrezo et al, 2009(Calavrezo et al, , 2010Kruppe and Scholz, 2014;Tracey and Polachek, 2018). Yet, these results should be interpreted cautiously because the counterintuitive result may be a direct consequence of the strong selection into STW-a bias that the matching and instrumental variable approaches of these studies probably only address partially.…”