Performance of digital to film mammography

CASE STUDY 2
 
Pisano and colleagues (2006) compared the performance of digital to film mammography for breast cancer screening. Now assume that the sensitivity and specificity of digital mammography is 85% and 95% respectively, the sensitivity and specificity of film mammography is 55% and 85% respectively, and that 0.03% of women below the age of 50 has breast cancer, and 12% of symptomatic women have breast cancer.
 
How successful is film mammography in identifying women with breast cancer?
According to this study, only 55% of all women who have breast cancer will be identified by this screening test.
 
 
How successful is film mammography in correctly ruling out the disease in women without breast cancer?
The test correctly identifies 85% of women without breast cancer.
 
 
Of all those without breast cancer, what percent will incorrectly test positive (false positives)? With a specificity of 85%, 15% of those without breast cancer will be false positives.
 
 
 
Suppose that you screened a population of 100,000 women under the age of 50 using both the digital and film mammogram. How confident would a woman who tests positive or negative be that she has breast cancer?