Concepts to be considered when appraising applicability of evidence to older people - levels of evidence

Definition

Levels of evidence - a hierarchy ranking study designs by their ability to minimise bias and establish causation, from systematic reviews/meta-analyses of randomised trials at the top to expert opinion/case series at the bottom

In geriatric medicine, high-level evidence (systematic reviews, large RCTs) specifically addressing frail or very old populations is comparatively scarce, meaning clinical decisions more often rely on lower-level evidence or extrapolation than in other fields

Study design determines susceptibility to particular biases: randomised controlled trials minimise selection bias and confounding via randomisation; observational studies (cohort, case-control) are more susceptible to confounding but can capture populations and outcomes (long-term, real-world) that RCTs often cannot

A lower level of evidence does not automatically mean a conclusion is wrong - it means the conclusion carries more uncertainty and is more susceptible to bias/confounding, and should be weighted accordingly, particularly when combined with other lines of evidence or strong biological plausibility
When high-level evidence in the relevant population is unavailable, transparently acknowledge the lower certainty of the evidence being relied upon, rather than presenting extrapolated or observational evidence with the same confidence as a well-conducted RCT would warrant

Systematic reviews and meta-analyses, randomised controlled trials, observational study design, expert consensus guidelines

Evidence hierarchies are a tool for judging certainty, not a rule for what to do - a well-conducted observational study addressing a directly relevant question in the actual population of interest can be more useful in practice than a highly-powered RCT conducted in a population that does not resemble the patient in front of you

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