Score contribution per author:
α: calibrated so average coauthorship-adjusted count equals average raw count
Heien and Wessells' two-step estimator for the multivariate sample-selection model has been used extensively during the past 15 years. A modified version of it, with slightly different selectivity regressors, has also appeared in the empirical literature. Both estimators are unfounded and generally do not correct for the sample selectivity bias as intended but have continued to gain popularity in empirical applications. The properties of the modified Heien-Wessells procedure are investigated in both the bivariate and multivariate contexts, and the conditions under which this estimator fails to correct for sample selectivity are examined. The theoretical properties are demonstrated with a simulated random sample.