In a quantitative review of human operant experiments, Kollins, Newland, and Critchfield (1997) found that humans are less sensitive to reinforcement contingencies than nonhumans are. Human performances were not as consistent with the matching law, and they were more variable from subject to subject. Some of the variables correlated with reduced human sensitivity were surprising. These included collection of the data under more controlled conditions (laboratory rather than naturalistic settings), and inclusions of discriminative stimuli correlated with alternative sources of reinforcement. We discuss these unexpected findings in the light of criticisms that have been leveled against meta-analytic literature reviews (e.g., the wisdom of grouping studies with widely diverse methods), and we suggest ways of improving future analyses of the behavior-analytic literature.