[The limitations of observational research].
van der Zee
Ate G J
AG
de Vries
Elisabeth G E
EG
Schaapveld
Michael
M
Willemse
Pax H B
PH
D019317:Evidence-Based Medicine; D006801:Humans; D019370:Observation; D016032:Randomized Controlled Trials as Topic; D012107:Research Design