Observational studies and randomized trials.
Kunz
R
R
Khan
K S
KS
Neumayer
H H
HH
D015982:Bias; D016022:Case-Control Studies; D015331:Cohort Studies; D006801:Humans; D015201:Meta-Analysis as Topic; D016032:Randomized Controlled Trials as Topic; D012107:Research Design