 Dionne and colleagues (2002) argued that significant effects of substitutes found in prior studies may be a statistical artifact due to "common-source bias", or bias occurring when independent and dependent variables are collected from the same person or group of people.In a study sampling 49 organizations, Dionne and colleagues controlled for the effect of common-source bias and found no moderating or mediating effects of substitutes on the relationship between leader behavior and group effectiveness.In a study by Podsakoff and Mackenzie (1995), the predictor variables, as well as the job attitude and role perception variables, were both taken from individual employees, while the performance measures were taken from supervisors.