When extrapolating from trial data to a particular context, it is important to compare the trial population to the target population. Given sufficient data, it is possible to examine treatment effect across important subgroups of patients. Then the trial results can be related to a specific sub-group, say with less severe disease than the average in the trial. One problem is that trial data are collected with greater diligence than routine data. Hence a suggestion to link trial data to routine data collected on the same patients. That way one can compare subgroups of trial and non-trial patients recorded in a broadly similar (i.e. routine) way. This strikes me as a half-way house to the day when (most) trial data are collected by routine systems, and trials are essentially nested within routine data-collection systems.
— Richard Lilford, CLAHRC WM Director
- Najafzadeh M, Schneeweiss S. From Trial to Target Populations – Calibrating Real-World Data. N Engl J Med. 2017; 376: 1203-4.