Background: In nonpsychotic parents and siblings of schizophrenic patients, the recurrence risk ratios of sustained attention deficits, as measured by the continuous performance test (CPT), were examined with a series of cut-off points.
Methods: Among 116 parents and 95 siblings of 91 schizophrenic probands in northern Taiwan, both undegraded and degraded sessions of the CPT were administered. Subjects' signal detection sensitivity of CPT performance (d') was standardized against a community sample without (unadjusted z score) or with (adjusted z score) adjustment for age, gender, and educational level.
Results: Differences in the risk ratios between the parents and siblings that were based on the unadjusted z scores of CPT d' diminished markedly if the adjusted z scores were used. As the cut-off point in the adjusted z score decreased from -2.5 to -3.0, the risk ratio increased continually for both the undegraded (10.1-18.8 for parents, 10.0-16.7 for siblings) and degraded (12.4-102.7 for parents, 8.6-72.0 for siblings) test.
Conclusions: Stringent cut-off criteria of CPT deficits with adjustment for demographic features leads to recurrence risk ratios greater than those based on schizophrenia alone in both parents and siblings of schizophrenic patients.