Intra-individual reaction time variability and all-cause mortality over 17 years: a community-based cohort study.
BACKGROUND
very few studies have examined the association between intra-individual reaction time variability and subsequent mortality. Furthermore, the ability of simple measures of variability to predict mortality has not been compared with more complex measures.


METHODS
a prospective cohort study of 896 community-based Australian adults aged 70+ were interviewed up to four times from 1990 to 2002, with vital status assessed until June 2007. From this cohort, 770-790 participants were included in Cox proportional hazards regression models of survival. Vital status and time in study were used to conduct survival analyses. The mean reaction time and three measures of intra-individual reaction time variability were calculated separately across 20 trials of simple and choice reaction time tasks. Models were adjusted for a range of demographic, physical health and mental health measures.


RESULTS
greater intra-individual simple reaction time variability, as assessed by the raw standard deviation (raw SD), coefficient of variation (CV) or the intra-individual standard deviation (ISD), was strongly associated with an increased hazard of all-cause mortality in adjusted Cox regression models. The mean reaction time had no significant association with mortality.


CONCLUSIONS
intra-individual variability in simple reaction time appears to have a robust association with mortality over 17 years. Health professionals such as neuropsychologists may benefit in their detection of neuropathology by supplementing neuropsychiatric testing with the straightforward process of testing simple reaction time and calculating raw SD or CV.
Centre for Mental Health Research, The Australian National University, Building 63 Eggleston Road, Canberra, Australian Capital Territory 0200, Australia.
Philip J
PJ
Batterham
David
D
Bunce
Andrew J
AJ
Mackinnon
Helen
H
Christensen
D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000523:psychology*; D001315:Australia / Q000453:epidemiology; D002423:Cause of Death; D003071:Cognition; D005260:Female; D015577:Geriatric Assessment; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008603:Mental Health; D009026:Mortality / Q000639:trends*; D009483:Neuropsychological Tests; D016017:Odds Ratio; D016016:Proportional Hazards Models; D011446:Prospective Studies; D011930:Reaction Time; D012307:Risk Factors; D013997:Time Factors
all-cause mortality; coefficient of variation; intra-individual standard deviation; intra-individual variability; older people; reaction time