Relative risk (RR) of false positive recall in relation to hormone replacement therapy (HRT) use, in various subgroups of women. *Relative to never-users, stratified by screening centre, age at screening, previous screening, body mass index, previous breast operation and time since menopause (where appropriate). Relative risks are shown as black squares with areas inversely proportional to the variance of the log relative risk, indicating the amount of statistical information available for that particular estimate. The corresponding confidence intervals (CI) are shown as horizontal lines. An arrow is used where the upper confidence limit exceeds the scale of the figure.