Extrapolation is often necessary when making decisions based on research evidence. This may be because certain types of people were not participants in studies (e.g. children). It may be because the treatments compared in studies were different from the treatment choices being made (e.g. the dose or duration of the treatment or expertise of the provider). Or it may be because the outcome that was measured was different from what is important to someone making a decision (e.g. the length of follow-up during which the outcome was measured). Applying research evidence always entails some degree of extrapolation and, consequently, requires an assessment of the applicability of the study results.
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