Positive predictive value
Why is it important? This is an indicator of the predictive validity of screening. The positive predictive value of a screening test is impacted by the prevalence of the disease in the target population. A screening test with a high positive predictive value will minimize unnecessary follow-up procedures since the test has a high likelihood of truly detecting the disease.
Indicator definition: The percentage of abnormal screens found to have breast cancer (invasive or in situ) after diagnostic work-up.
Target:
- Initial screens: ≥5%
- Subsequent screens: ≥6%
Measurement timeframe:
- January 1, 2019 to December 31, 2019
- January 1, 2020 to December 31, 2020
Indicator calculation:
- Numerator: The number of abnormal screens found to have breast cancers (DCIS or invasive) within 6 months of screens.
- Denominator: The total number of abnormal screening mammograms in the measurement timeframe.
- Exclusions: Abnormal breast cancer screens of individuals that were lost to follow‐up within 6 months of screening.
Additional considerations: While this indicator is useful in providing information on the performance of the screening program, it should be interpreted in context with other factors such as the cancer detection rate (CDR) and abnormal call rate (ACR).
Percentage of individuals (aged 50-74) with abnormal mammograms who were diagnosed with breast cancer, by jurisdiction — 2019 and 2020
Data table and footnotes
The positive predictive value (PPV) within individual jurisdictions remained relatively consistent in both 2019 and 2020. It ranged from 4.8% to 13.4% in 2019 and 5.8% to 11.8% in 2020.
Percentage of individuals (aged 50-74) with abnormal mammograms who were diagnosed with breast cancer, by jurisdiction and age group — 2019 and 2020
Data table and footnotes
Across most jurisdictions, the PPV increased in each successive age group in both 2019 and 2020. In 2020, PPV in the youngest age group (50-59) and oldest age group (70-74) ranged from 4.2% to 7.4% and 8.6% to 22.2% respectively. The increase in PPV with an increase in age could be due to several factors such as: the increase in incidence with age, increase in screening history in older population cohorts and improved interpretive ability because of older women having less dense breast tissue.
Percentage of individuals (aged 50-74) with abnormal mammograms who were diagnosed with breast cancer, by jurisdiction and screening sequence — 2019 and 2020
The PPV for initial screens remained relatively consistent across most jurisdictions, ranging from 3.8% to 9.9% in 2019 and 3.9% to 6.1% in 2020.
The PPV for subsequent screens ranged from 4.8% to 16.8% in 2019 and 5.8 to 15.3% in 2020. In most of the jurisdictions, the PPV for subsequent screens was higher than initial screen. This is perhaps because previous screens can establish a baseline for comparison for subsequent screens, resulting in fewer false-positive abnormal calls. Most jurisdictions met the Canadian target of ≥6% for subsequent screens in both 2019 and 2020.