CRITICS of observational studies, even those that employ sophisticated statistical models to address issues around selection bias, are quick to challenge any hard claims to causation. Even more tenuous are the claims from epidemiological studies. These critics like to compare these studies to the astronomical observations of Ptolemy, who could predict the motions of stars with great accuracy but completely misinterpreted their meaning.The article by Professor Gill and colleagues in this issue of the Journal (1) raises an intriguing observation-namely, that losing the ability to bathe oneself is associated with a higher likelihood of a long-term admission to a nursing home. One might be content to acknowledge this risk factor and move on. After all, any geriatrician knows that bathing is an early-loss Activity of Daily Living (ADL) (2). However, the authors, after warning about confusing association and cause, use these findings to suggest that efforts directed toward interventions intended to prevent and remediate bathing disability have the potential to reduce the burden and expense of long-term care services. Now that sounds pretty causal.
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