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Understanding Medical Articles and Reports Linda Vincent, MPH UCSF Breast SPORE Advocate September 24, 2005 [email protected] 510-527-6720 Introduction to Statistics Mean, average of a set of numbers or values Median, the number closest to the middle of a set of numbers Standard Deviation, information on the spread of the numbers from a complex calculation More Statistics Probability, p-value, comparing sets of numbers from research in another complicated calculation that gives information on statistical significance p<.05 is the same as 95% Confidence Intervals Answers question like, how likely is it that people in the study that got the investigational drug got better because the drug did its job, or whether they got better due to some other factor. Risk Ratio Relative Risk or Risk Ratio, RR is used widely in research papers. Compares the probability of an outcome among individuals who have a specific “exposure” or a specific characteristic to those who have not been exposed RR is calculated in Cohort or Experimental studies (Clinical Trials) Calculating Relative Risk 2 X 2 Table, see page 51 of Cook Article, Lung Number with disease Number without disease Number of exposed 90 19,846 Number of unexposed 115 19,827 Calculating Relative Risk-2 RR Calculation: RR = Absolute risk in exposed participants Absolute risk in unexposed participants 90/19,934 115/19,942 RR = 0.78 CI = 0.59-1.03 p-value = .08 Interpretation of RR RR equal to or greater than one, written as =>1 The higher the number above one the greater the risk/disease is associated with the exposure RR =< 1 There is no association of the risk/disease to the exposure RR = 1 The risk is the same in both groups Interpretation of Confidence Intervals Confidence Intervals, CI 95% CI is current standard If the CI does not include 1.0 that the RR is statistically significant Previous example in the Cook article, CI = 0.59-1.03 Odds Ratios Case-Control Studies can’t use RR because the OR, Odds Ratios are an estimate of RR Number with disease (cases) Number exposed Number not exposed Number without disease (controls Absolute Risk Absolute Risk gives an actual number of health problems that happened or were prevented due to a drug Doctors and patients have difficulty understanding RR and OR Use of NSAIDS and Risk of Breast Cancer: The CaseControl Surveillance Study Revisited Advantages of Case-Control Studies: Less expensive and time-consuming than cohort studies especially with rare diseases Odds Ratio can be used to estimate the Risk Ratio Use of NSAIDS and Risk of Breast Cancer: The CaseControl Surveillance Study Revisited Disadvantages of Case-Control Studies: Cases and Controls may come from different groups which will bias the results Time-related relationships may be difficult to ascertain There is the always the possibility of recall bias when asking about exposures that occurred in the past Use of NSAIDS and Risk of Breast Cancer: The CaseControl Surveillance Study Revisited What is the purpose of the study and what question did the authors address? See first sentences of the abstract What were the unanswered questions raised by prior scientific work that led to this study? The meta-analysis of Khuder and Mutgi found an 18% decreased risk in regular NSAIDs users in 8 case-control studies. Critical Evaluation of Zhang Article, Continued Do the authors state a hypothesis? If so what is it? Hypothesis is a statement of belief used in the evaluation of population values. Hypothesis statement: There is an association between the exposure and the outcome. No hypothesis statement in the Zhang article Zhang, continued What are the results? Table 1-For the most relevant category, regular use of NSAIDs, OR was 0.78, 95% Confidence Intervals (CI) 0.63-0.97 CI dosen’t include 1.0 Table 2-Longer duration of regular NSAIDs use was associated with a lower risk of breast cancer, pvalue for trend was 0.02 Table 3-Looked at differences between aspirin, Ibuprofen, and NSAIDs (p-value for trend, not significant) Zhang, continued What are the conclusions drawn from the results? Are the conclusions supported by evidence in the article? First paragraph under DISCUSSION, “Our results suggest a modest decrease in the risk of breast cancer associated with regular NSAIDs use….” Last paragraph, “In summary, the present study found…the effect is relatively weak. Given the conflicting results from large cohort studies…too early to suggest that regular use of NSAIDs could help prevent breat cancer.” Zhang, continued What methods did the authors use? Cases were selected from patients living within one hour driving distance to the hospitals Cases were interviewed by trained nurse interviewers using structured questionnaires Controls… Data analysis, relationships of use to risk performed with multiple logistic regression models Zhang, continued What are the strengths of the paper? Researchers/authors attempted to validate previous studies on use of NSAIDs and reducing risk of breast cancer Note on biological mechanism for reducing risk Note on inconsistencies from other studies Zhang, continued Are there obvious problems with the article? The hormone receptor status of the tumors was obtained from only 26% of the cases. Other risk factors for breast cancer were not evaluated, but were similar among cases with data on hormone status suggesting absence of selection bias What additional experiments would strenghten the authors conclusions? Are the findings significant? If so, for who? Resources Free subscription services BreastCancer.Net, http://breastcancer.net Amedeo.com, http://amedeo.com Medscape, http://www.medscape.com PubCrawler, http://pubcrawler.gen.tcd.ie Resources continued… National Cancer Institute Pub Med, http://pubmed.gov MedLinePlus, http://medlineplus.gov FDA Center for Drug Evaluation and Research http://www.fda.gov/cder Guidelines National Comprehensive Cancer Network, http://nccn.org San Antonio Breast Cancer Symposium http://sabcs.org American Society of Clinical Oncology http://asco.org Project LEAD http://natlbcc.org or Google National Breast Cancer Coalition Check left column links, click on Education and Training, and click again on Project LEAD