Pediatricians' and psychologists' implicit personality theory: significance of sibling differences.

Pediatricians' and psychologists' implicit theories of how personality develops are compared to recent behavioral-genetic analyses based on twin and adoption studies. Results show that both practitioner groups--less so the psychologists--underestimate differences between children in the same family, over-estimate the influence of their shared environmental experiences, and underestimate those not shared. Findings mirror the bias of traditional personality research, pointing out the need to investigate environmental variables with differential impacts on children in the same family, e.g., sibling deidentification; one child extrovert, one introvert; one saint, one sinner.