*Univariate odds ratio (OR) not reported but calculated from the figures given; ‡contacted for confirmation of figures published; ‡univariate OR not calculated because of empty cell; §excluding Carpenter’s multi-centre European study as this includes some or all of the data from studies conducted by Helweg-Larsen, Schellscheidt, Fleming and L’Hoir; ¶pooled univariate OR using the Mantel-Haenszel estimate; **pooled adjusted OR using ln (effect size) and SE (ln (effect size)); ††adjusted for sex and age; ‡‡adjusted for centres, infant age, gender, multiple birth, birthweight, parity, admission to special care baby unit, sleeping position, bed sharing, dummy use, history of an apparent life threatening event, maternal smoking, others smoking in the household, marital status, employment and urinary tract infection during pregnancy; §§adjusted for sleeping position, breastfeeding, heavy maternal smoking, maternal social status, alcohol consumption during pregnancy and whether a cushion was used for the last sleep; ¶¶adjusted for infant age, gestational age, birth centile, parity, parental unemployment, moving house, bed sharing, room sharing, sleeping position, pacifier use, use of duvet, postnatal exposure to tobacco, maternal alcohol consumption, length of previous sleep, previous apparent life threatening event, recent illness and change in infant routine; ***adjusted for maternal age, marital status, education and index of prenatal care; †††adjusted for infant age, parity, maternal age at first live birth, birthweight, sex, socio-economic status and maternal smoking during pregnancy; ‡‡‡gender and socio-economic status.