An analytical review was conducted on the expectancy theory literature in order to determine for each of two effort and four performance criteria (across studies and controlling for two methodological factors) whether the accuracy of the theory's predictions is an inverted-U-shaped function of the number of outcomes used to derive measures of motivational force, and whether this curve has its point of inflection at outcome set size 10-15. The results revealed that Self-Reported Effort conforms to the inverted-U pattern when validity coefficients are averaged within outcome set size categories, but no evidence of the ascending portion of the curve was found when the relationship was measured by a Spearman ρ for the range 1-14 of set size. For every other criterion, validity of prediction decreased as number of outcomes increased, and this was observed in averages as well as ρ's. The possibility that an inverted-U-shaped curve has its point of inflection at about outcome set size 5 is not ruled out by these results, however. Results were discussed in terms of the concepts of number of outcomes causing motivational force and measurement error attributable to outcome irrelevance. © 1979.