In the UKwomen aged from 47 to 73 are invited for mammography screening every 3 years to detect early signs of breast cancer. This involves taking twomammograms (x-rays) of each breast. Each woman’s mammograms are examined by two separate readers, and if there are suspicious abnormalities the woman is recalled for further tests. The readers are qualified either as breast screening radiologists or radiography advanced practitioners. Mammography has neither perfect sensitivity of specificity, so some cancers are missed (false negatives) and some women who do not have cancer are recalled for further tests (false positives).