Extended Data Fig. 1: Dunedin Study attrition analysis using IQ.
No significant differences in childhood IQ were found between the full cohort, those still alive, those seen at Phase 45, or those scanned at Phase 45. Those who were deceased by the Phase 45 data collection had significantly lower childhood IQ’s than those who were still alive (t = 2.09, p = 0.04). Center lines of boxes represent the median. Lower and upper hinges of boxes represent the 25th and 75th percentiles. Whiskers show the range. The red line connects the means of each distribution. We report childhood IQ because it is known to be a strong predictor of late-life health outcomes, as shown by many cohort studies from many nations. Childhood IQ predicts health and social outcomes in adulthood, and these outcomes include physical functions, cognitive decline, mental health, inflammation, metabolic syndrome, disease incidence, dementia, mortality, and also neuroimaging-based, genomic, and epigenetic indicators of health. Based on the literature, we report three groups: study members who died before age 45, and thus could not have taken part in data collection, study members who were alive and thus could take part, and study members who actually did take part. We compared these three groups to the original birth cohort. The figure shows that the small group of study members who had died before age 45 had significantly lower mean childhood IQ as a group. Some of the early deaths were Dunedin Study members who had more disadvantages in their lives leading to poorer health and increased risk of early mortality. Study members who died of childhood diseases may have been already unwell at the time of IQ testing, which could have lowered their scores. However, cohort members who are still alive and cohort members who took part in data collection did not differ from the full original cohort on their mean childhood IQ; they still represent population variation on this key health risk factor. Abbreviations: IQ = intelligence quotient.
