Changes in white matter as determinant of global functional decline in older independent outpatients: three year follow-up of LADIS (leukoaraiosis and disability) study cohort.

11 12 Assuming that the group with the mildest degree of age related changes in white matter has a 25% risk of transition to disability or death over three years (equal to that of the general older population), we needed 800 people to show a significant trend (1.7 estimated relative risk) in the effect of exposure to the three increasing degrees of severity, with adjustment for age, reasons for presentation, and comorbidity (α error probability 5% (two tailed), power 80%).

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