Sojourner, A., B. Frandsen, R. Town, D. Grabowski & M. Chen (2015) Impacts of Unionization on Quality and Productivity: Regression Discontinuity Evidence from Nursing Homes. ILR Review. 68(4): 771-806. [Appendix]  
IZA & NBER  

• Hamilton Project: The Shift in Private-Sector Union Participation
• Vox.com: I was skeptical of unions. Then I joined one.