What is recall bias?

Researchers investigated whether sleep practices in pregnant women were associated with risk of late stillbirth.1 A case-control study design was used. Cases were 155 women with a singleton late stillbirth (without congenital abnormality) that occurred at 28 weeks’ gestation or later. Cases were identified by clinicians at participating maternity units and were also recruited from a registry. Controls were 310 women with single ongoing pregnancies. Controls were matched to cases on stage of gestation when the stillbirth occurred. Information about sleep practices, including maternal snoring, daytime sleepiness, and sleep position at the time of going to sleep and on waking (left side, right side, back, and other) was obtained through questionnaires that were administered by interviewers. The women who served as cases were interviewed in the first few weeks after stillbirth and asked about their sleep practices the night before stillbirth occurred (when the baby had probably died); controls …