2. List of study design features.

Question and checklist	RCT	PCS	RCS	NCC	CC
Was there a comparison:
Between two or more groups of participants receiving different interventions?	Y	Y	Y	Y	Y
Within the same group of participants over time?	P	N	N	N	N
Were participants allocated to groups by:
Concealed randomization?	Y	N	N	N	N
Quasi‐randomization?	N	N	N	N	N
Other action of researchers?	N	N	N	N	N
Time differences?	N	N	N	N	N
Location differences?	N	P	P	NA	NA
Treatment decisions?	N	P	P	N	N
Participants' preferences?	N	P	P	N	N
On the basis of outcome?	N	N	N	Y	Y
Some other process? (specify)
Which parts of the study were prospective:
Identification of participants?	Y	Y	N	Y	N
Assessment of baseline and allocation to intervention?	Y	Y	N	Y	N
Assessment of outcomes?	Y	Y	P	Y	N
Generation of hypotheses?	Y	Y	Y	Y	P
On what variables was comparability between groups assessed:
Potential confounders?	P	P	P	P	P
Baseline assessment of outcome variables?	P	P	P	N	N

RCT = randomized clinical trial
 PCS = prospective cohort study
 RCS = retrospective cohort study
 NCC = nested case‐control study
 CC = case‐control study
 Y = yes
 N = no
 P = possibly
 NA = not applicable