As he notes however, due to the interaction between the two, no casual interpretation of this trend can be made. The interaction that Sylos-Labini was addressing was that of the transfer of costs onto prices. Longer tenure means a more experienced workforce. Union emphasis on seniority gives experienced workers an incentive to train new workers. Statistical analysis may not allow for higher quality from a union work force.
Management is forced to demand more of union workers.
An increase in the supervisor to worker ratio. Better monitoring of worker performance. This conclusion is drawn from the results of a study by Kim B. Clark which Reynolds cites. This is a reference to burdensome work rules that labor unions have insisted upon. It can be argued that the intention of such rules is not to provide for increased safety, greater efficiency, job protection, or anything other than increasing employment for members of the union.