SCREENING & DIAGNOSIS TEST EVALUATION

Screening and Diagnostic Test Evaluation
Maximum length: 2500 words

• Please note that you are not expected to undertake a literature review to answer these questions. Refer to your course notes or other readings if you wish but detailed further reading is not required.

You must complete your assignment alone. Submitting assignments which have been jointly done is not acceptable. Copying someone else’s work or quoting from text without adequate attribution of the source is plagiarism and is not acceptable. All assignments will be verified by plagiarism detection software. Penalties will be applied for plagiarism.

*Breast cancer is a malignant tumour that starts in the cells of the breast and is mostly found in women. The most common symptom of breast cancer is a new lump or mass. Breast cancer is sometimes found after symptoms appear, but some women with early breast cancer have no symptoms. If an abnormality is found during a test, or if a patient has a symptom of breast cancer, biopsy and histologic examination is used to diagnose the disease. In the late 1980s, many developed countries began to introduce population based screening mammography. Over the past decade, most screening mammography programs have replaced film mammography with digital mammography. This was largely based on evidence from the following article:

Pisano ED et al. Diagnostic Performance of Digital versus Film Mammography for Breast- Cancer Screening. The New England Journal of Medicine 2005;353(17):1173-1783. http://www.nejm.org/doi/abs/10.1056/NEJMoa052911?url_ver=Z39.88-

2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dwww.ncbi.nlm.nih.gov

 

Please read the article by Pisano et al NEJM 2005, and use it to answer ALL the questions below. You do not need clinical knowledge or to refer to the detailed account of the design of this trial published previously in order to answer the questions. You do need to justify your opinion and discuss how it might introduce bias and possibly affect the test performance and/ or results.

1. Are the criteria for inclusion appropriate (population, prior tests)? (2 mark)
2. Were the tests evaluated in an appropriate spectrum of patients? (2 mark)
3. What is the reference standard of this study? (1 mark)
4. Is the reference standard likely to correctly classify the target condition? Please explain the implications, if any, of the researchers’ choice. (4 marks)
5. Were the tests independent of (i.e. not incorporated in) the reference standard? (4 marks)
6. Were the same clinical data available when test results were interpreted as would be available when the test is used in practice? (3 marks)
7. Were test results interpreted without knowledge of the results of other tests? (2 marks)
8. Did all patients (or a random selection) receive verification using a reference standard of diagnosis? (4 marks)
9. Did patients receive the same reference standard regardless of the test result? (4marks)
10. Were uninterpretable and/or intermediate test results reported? (2 marks)
11. Were withdrawals from the study explained? (2 marks)
12. Was the time period between index test and reference standard short enough to be reasonably sure that the target condition did not change between the two tests? (3 marks)
13. When interpreting digital and film screening mammograms findings and results for each patient, radiologists rate the mammograms using the Breast Imaging Reporting and Data System (BIRADS) score. In this system, the results are sorted into categories numbered 0 through 6. A BIRADS score of 0 indicates incomplete data, a score of 1 negative results, a score of 2 benign findings, a score of 3 findings that are probably benign, a score of 4 the presence of a suspicious- appearing abnormality, and a score of 5 findings highly suggestive of cancer. In the analyses, scores of 0, 4, and 5 are defined as positive for a breast abnormality and scores of 1, 2, and 3 are defined as negative for a breast abnormality.

Please use the BIRADS Score and raw data from Table 4 of the Pisano 2005 paper to calculate the following measures of diagnostic accuracy for all breast cancers in all women.

1. a) For digital mammography recalculate the appropriate expressions of diagnostic accuracy from the data presented in Table 4:

1. Draw a 2×2 table comparing digital mammography to the reference standard; (2 marks)
2. Calculate Sensitivity and specificity; (1 mark)
3. Positive and negative predictive value; (1 mark)
4. Positive and negative likelihood ratios. (1 mark)

1. b) For film mammography recalculate the appropriate expressions of diagnostic accuracy from the data presented in Table 4:

1. Draw a 2×2 table comparing film mammography to the reference standard; (2 marks)
2. Sensitivity and specificity; (1 mark)
3. Positive and negative predictive value; (1 mark)
4. Positive and negative likelihood ratios. (1 mark)

 

YOU MUST SHOW ALL WORKING AND CALCULATIONS

14. Government in a developed country wish to screen women for breast cancer using digital mammography, where the underlying prevalence of disease is 15% in the population. Compare the positive and negative likelihood ratios for the test and discuss the implications of a positive test result and a negative test result for breast cancer in this setting? (3 marks)
15. Government in a developing country wish to screen women for breast cancer using film mammography where the underlying prevalence of breast cancer is 1% in the population. Compare the positive and negative likelihood ratios for the test and discuss the implications of a positive and negative test result for breast cancer in this setting? (3 marks)
16. Compare your answers for questions 14 and 15 and discuss why you think they are/ are not different. (1 marks)