jobs to yield better fits between their abilities and job demands (e.g., Swaen et al., 2002). There are probably many cases of accommodative activities in place throughout the workforce.

The existing scientific literature has significant limitations intrinsic to population surveys, field studies, and laboratory experiments. We often rely on metanalytic studies, for example, to help ensure better inference, but these have weaknesses, for instance, the choice of rules for inclusion and exclusion of studies in the analysis and the fact that studies with nonsignificant findings tend not to be published. However, metanalyses do provide an efficient way to estimate effect sizes across studies (e.g., Schmidt, 1996).

An important theme is the need to consider increased age as contributing to counterbalancing trends. Aging processes tend to lower overall general functional capacity. Increased age is also associated with increased experience that tends to raise experience-related functional capacities. These two aspects of age may trade off, particularly when experience leads to skill and expertise, a point stressed in some of the earliest literature in this field (e.g., Welford, 1958).

Training and Retraining

Training and retraining seem particularly relevant for older workers, who are likely to be the most distant from initial professional training and from initial job training (Sparrow and Davies, 1988). Whether older workers are particularly in need of training and retraining can be addressed from the perspective of two outcome criteria: productivity and safety. To the extent that age discrimination exists in work settings, it may be driven by perceptions that older workers are less productive.

Productivity

Cross-sectional metanalyses show no relation between age and job productivity (McEvoy and Cascio, 1989; Waldman and Avolio, 1986). This outcome is surprising in view of the ubiquitous laboratory-based findings of age-related declines in basic perceptual and cognitive abilities and in problem-solving performance on novel tasks (see Chapter 5). Productivity is typically measured using work output measures or peer and supervisor ratings of performance. One explanation for the apparent lack of an association between age and productivity is that, as mentioned previously, increased age is associated with the acquisition of job-specific knowledge and skills that compensate for age-related declines in general abilities (Salthouse and Maurer, 1996).

Another possibility is that the cross-sectional comparisons involve a mix of younger workers with varying skills and older workers with estab-



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