How "regular" is sentence comprehension in Broca's aphasia? It depends on how you select the patients

Grodzinsky, Piñango, Zurif, and Drai (1999) argue that a statistical analysis of pooled sentence comprehension data from published studies of Broca's aphasic patients supports the dominance of a differential pattern of performance on active and passive voice structures. They argue that these results counter a previous study in which individual patient data from published studies were analyzed. However, Grodzinsky et al. have not carried out a true test of their hypothesis, but have biased the outcome by selecting samples for analysis that support their claims.