Score contribution per author:
α: calibrated so average coauthorship-adjusted count equals average raw count
This is a response to [Jordahl, H., Poutvaara, P., & Tuomala, J. (2009). Comment on education returns of wage earners and self-employed workers. Economics of Education Review 28]. We acknowledge that econometrics have improved since the time our original paper was written, so that the choice of accurate instruments is now more deeply founded. However, in this note, we argue that the differences in the estimates obtained by Jordahl et al. (2009) has been generated not only because the "sensibility of HT estimators to the choice of instrumental variables", but also to the estimation metholology followed by them, in which rarely changing variables are considered to be time-varying.