Retention and longitudinal change in Insight 46, an intensive neuroscience sub-study of the 1946 British birth cohort.

The overall retention rate in Insight 46 was 88% over approximately 2.5 years of follow-up.

• Of 502 participants assessed at baseline, 442 returned for follow-up.
• Mean (SD) age at baseline was 70.5 (0.7) years.
• Mean (SD) follow-up interval was 2.5 (0.3) years.
• 14 participants were deceased by the time of follow-up, 12 of whom were female.

β-amyloid positivity, female sex, and older age at baseline were each associated with lower odds of retention.

• β-amyloid status was measured using positron emission tomography (PET).
• These three factors were identified as independent predictors of non-retention.
• Of the 14 deceased participants, 12 were female, suggesting mortality contributed to lower female retention.
• These associations have implications for the generalisability of longitudinal findings from this cohort.

Completion of neuroimaging and better cognitive performance at baseline, particularly on memory testing, were associated with higher odds of retention.

• Better performance on memory testing specifically was among the stronger baseline cognitive predictors of retention.
• Neuroimaging completion at baseline also related to higher odds of returning for follow-up.
• This pattern suggests a 'healthy volunteer' bias may influence retention in neuroscience sub-studies.
• These findings have implications for the interpretation and generalisability of Insight 46 data.

Improvements were observed in certain cognitive tests over the follow-up period while declines were seen in others.

• Improvements were noted in the face-name test and logical memory delayed recall.
• Declines were observed in the mini-mental state examination (MMSE) and digit-symbol substitution test.
• The follow-up interval was mean 2.5 (SD 0.3) years.
• Mixed directional changes suggest a combination of practice effects and genuine cognitive decline across different domains.

Increases in self- and informant-reported cognitive complaints, cognitive disorder diagnoses, and motor abnormalities were observed over the follow-up period.

• Both self-reported and informant-reported cognitive complaints increased over 2.5 years of follow-up.
• The number of cognitive disorder diagnoses increased between baseline and follow-up.
• Motor abnormalities also increased in frequency over the follow-up interval.
• These longitudinal clinical changes occurred in a cohort with mean baseline age of 70.5 years.

Declines in blood pressure were observed over the 2.5-year follow-up period.

• Blood pressure declined between baseline and follow-up assessments.
• This finding was observed alongside increases in cognitive complaints and motor abnormalities.
• The cohort had a mean age of 70.5 years at baseline, placing them in a late-life period when blood pressure changes are clinically relevant.
• The authors noted this as one of the clinical changes with implications for interpretation of longitudinal data.