Before. And after

In the world of non-randomised studies, there are bucketloads of variants, a common one that we see is the ‘before and after study’. This is, on the face of it, a sensible approach. Do your ‘thing’, then change stuff, do the ‘other thing’. Monitor something important you hope to change, and then if it does, you have some evidence of benefit.

Except for most before and after studies it’s not quite like that. They are rarely conducted prospectively, but usually because Something is going on—rising infection rates, loads of Kawasaki diagnoses, increasing ‘do not attend’ rates—and Something Must Be Done. So it is. And then the worrying thing falls back down …