Dr. Clancy McKenzie’s work relied on observational and retrospective analyses, not controlled experiments. For example, he correlated schizophrenia with early separations (e.g., hospitalizations or sibling births) using medical records and patient histories (). His 1966 observations, inspired by Margaret Mahler, noted that many schizophrenic patients had a sibling born when they were around 18 months old, suggesting maternal inattention as a trauma.