EPID600 (Spring 2013) module Questions for Case Study on Mammography in Asia (View instructions) (NOTE: For some of these questions there may not be one "right answer".)
1. A program using screening mammography, as described in the Leung et al. article, is best regarded as: (Choose one best answer)
2. For a disease to be a suitable candidate for a screening program, it must be a serious public health problem and have a suitable natural history. Which component of natural history (for a non-infectious disease) is essential? (Choose one best answer)
3. A hypothetical observational breast cancer study enrolled 10,000 women age 50 years and older during 1990 and followed each woman for 10 years. All women received a free medical exam, including a mammogram, at baseline and each year thereafter. All deaths were fully investigated, and there was no loss to follow-up. At the baseline examination, 80 women were diagnosed as having early breast cancer. 20 of these women died during the 10 year follow-up. By the end of follow-up, 240 other women had developed breast cancer, including 30 who died from their disease. 200 other women (who did not develop breast cancer) died from other causes. Answer the following questions based on this information (suggestion: drawing a flow chart may help). Show calculations, give answers to 3 significant figures, and show units.
4. In order to make projections of potential benefit of mammographic screening programs for women in Asia, Leung et al. carried out a meta-analysis of randomized controlled trials of the effectiveness of mammographic screening in reducing mortality from breast cancer. The authors excluded from their meta-analysis studies that enrolled primarily symptomatic patients with breast lumps, pain, nipple discharge, or enlarged lymph nodes (p1841, middle column). Briefly explain the rationale for this exclusion. 5. Depending on their study design, evaluations of the efficacy of breast cancer screening programs are vulnerable to three phenomena related to the nature and natural history of the disease: a) lead time bias, b) length bias, and c) overdiagnosis bias. For each of these types of bias give a succinct statement of what this bias is and explain whether it is a concern (and if it is, how the bias could occur) in studies that analyze breast cancer mortality in women randomly assigned to a screening group or a non-screening group.
6. The American Cancer Society (ACS) publication Cancer Facts & Figures, 2003 (http://ww3.cancer.org/downloads/STT/CAFF2003PWSecured.pdf) gives the annual incidence of invasive female breast cancer in the U.S. as 136.7 per 100,000 women during 1995-1999 (adjusted to the 2000 U.S. standard population), whereas in Figure 2 (in Leung et al.) the annual incidence of invasive breast cancer is above 300 per 100,000. What is the most likely explanation for this difference? 7. “In Hong Kong, there were 868 new cases of breast cancer for women aged 50 years or more in 1996, an incidence of 123.3 per 100,000.” (p1843, left col. - note that “50 years or more” includes women over 69 years of age). If the incidence rate of 123.3 per 100,000 women-years is a crude rate (i.e., not standardized), what was the approximate number of Hong Kong women in this age group in 1996? (3 significant figures) 8. The authors give an estimate of 146.1 per 100,000 women for Hong Kong’s projected breast cancer “prevalence ratio” at screening (p 1843, left col., bottom). 8a. Derive the authors’ estimate. 8b. Use the prevalence estimate (146.1 per 100,000 women age 50+ years) to estimate the number of cases of breast cancer that would be available to detect with the screening program if there were 700,000 women age 50+ years old in Hong Kong in 1996 and all participated? 9. At the top of the middle column of page 1843, the authors project a range for the PPV for screening in Hong Kong women (1.8% to 13.4%). This question asks you to derive that range, step by step, and to interpret it. 9a. Use your answer to question 8 to derive low and high estimates of the number of cases that would be detected based on the “optimal ranges” stated at the bottom of page 1843, column 1. 9b. Use your answer to question 8 and the “optimal ranges” to derive low and high estimates for the number of women without breast cancer correctly classified as such (i.e., “true negatives”) if there were 700,000 women age 50 years or more in Hong Kong in 1996 and all were screened. 9c. Using your answers above, derive the range for PPV. 9d. Show the source of the percentages in the authors’ statement “So we would expect at least 86% and as many as 98%, of positive screens to be false positives.” (page 1843, top of column 2). 10. On page 1842 (right column), the authors state that “the case detection rate (i.e., screen-detected cancers plus interval cancers) in the screened group is the best proxy available for the prevalence of the condition at screening.” Which of the following conditions do the authors include in their usage of “the condition”? Indicate all that apply.
11. The cumulative false-positive rate cited to Elmore et al. (p1844, middle col.) corresponds to a cumulative specificity of only 50.9%. Why is that specificity so much lower than the range of 93.5%-99.1% cited on page 1843, bottom of left column? 12. “Miller et al. argued that the excellent survival (87.5% alive at 10 years) of women with DCIS and early impalpable invasive cancer in CNBSS II was almost certainly due to a combination of lead time and length bias.” (middle of left col. on p1844) In 1-3 sentences, express this statement in a manner that an educated person who had never encountered epidemiology would understand (refer to “DCIS and early impalpable invasive cancer” as “very early breast cancer”).
2/16/2007vs, 9/26/2009vs, 2/13/2012vs |