Portela, Miguel, R.  Alessie, and C.N.  Teulings. ?Measurement Error In Education And Growth Regressions?. Scandinavian Journal Of Economics 112. Scandinavian Journal Of Economics  (2010): 618-639.

Portela, Miguel. ?Measuring Skill: A Multi-Dimensional Index?. Economics Letters 72. Economics Letters  (2001): 27-32.