I haven't reviewed the methodology of this first hit in detail, but here's perhaps some: https://www.researchgate.net/profile/Charles-Knutson/publication/426172

I haven't reviewed the methodology of this first hit in detail, but here's perhaps some: https://www.researchgate.net/profile/Charles-Knutson/publication/4261726_Do_Programming_Languages_Affect_Productivity_A_Case_Study_Using_Data_from_Open_Source_Projects/links/546223460cf2c0c6aec1a663/Do-Programming-Languages-Affect-Productivity-A-Case-Study-Using-Data-from-Open-Source-Projects.pdf https://www.researchgate.net/profile/Charles-Knutson/publica... I don't think it's this one but I do remember reading a very high quality study arriving at the same result as well.