For an introduction to instrumental variables, which is the approach used by Lorenzo Coviello et al. (2014), see Angrist and Pischke (2009) (less formal) or Angrist, Imbens, and Rubin (1996) (more formal).
Fir eng Introduktioun u Instrumentalvariablen, déi d'Approche vum Lorenzo Coviello et al. (2014) , kuck Angrist and Pischke (2009) (manner formell) oder Angrist, Imbens, and Rubin (1996) (méi formell).