Figure 1. A mathematical model of breast cancer screening consisting of 12-month cycles of 10 health states that simulate the theoretical natural history of breast cancer, comprising the following seven structures: u₁: healthy; w₁: false positive; u₂–u₅: undetected breast cancer (stages 1–4); w₂–w₅: detected for breast cancer (stages 1–4) through screening or outpatient care; du₁: died from a cause other than breast cancer; du₂–du₅^a: undetected and died of breast cancer; dw₁–dw₄^a: detected and died of breast cancer. Stage classifications used here are those published by the Union for International Cancer Control (UICC) for Japanese data and by the American Joint Committee on Cancer (AJCC) for United States data. ^aDeath from causes other than breast cancer (μ) is excluded. BC, breast cancer.