Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
D1: Clear aims and objectives, D2: study design quality, D3: sample size justified, D4: target population clearly defined, D5: appropriate population
Red circles: high risk of bias, yellow circles: unclear; green circles: low risk of bias
