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Zahra Abdalla MPH 510 – Applied Epidemiology Dr. Boye Cigarette Smoking and Lung Cancer Question 1: What makes the first study a case-control study? The first study is a case-control participants are selected based on the disease and individual with the disease are compares individuals without the disease. In this study patients diagnosed with the lung cancer and the patients of other disorders and without the disease were included in the study. Also according to Friis and Sellers (2014), case-control study uses one point observation (hospital) which is mention in this study. Question 2: What makes the second study a cohort study? The second study is cohort study because the study was followed over period of time. In this study individual’s information about past smoking behaviors were obtained from different sources and time. Question 3: Why might hospitals have been chosen as the setting for this study? CDC / EIS Summer Course 2003: Smoking and Lung Ca - Student's Guide Page 3 Using a hospital setting for case -control study for one observation area ensure accuracy. In this study it was perhaps easy to track patients information, and easy to recall exposures. Question 4: What other sources of cases and controls might have been used? As stated by Friis and Sellers,(2014), other sources that is helpful for cases and controls are a disease registry, Medical records, and disease statistics. I would like think other sources that could have been is using other population such as older adults who are in nursing homes. Question 5: What are the advantages of selecting controls from the same hospitals as cases? The advantages selecting controls from the same hospitals as cases could mean that the individuals are easy to locate. Also since they are based on one location there is time saving and cost effective to track the individual’s medical records. Question 6: How representative of all persons with lung cancer are hospitalized patients with lung cancer? It is difficult to say hospitalized patients with lung cancer was probably representative of all persons with lung cancer. Because not all patients with who are hospitalized with lung cancer represent all cases in the general population. Question 7: How representative of the general population without lung cancer are hospitalized patients without lung cancer? Hospitalized patients without lung cancer could mean they have other health conditions than those of the general population. At the same time it is difficult to state how much of date hospitalized patients without lung cancer represent or similar to patient general population without lung cancer. Question 8: How may these representativeness issues affect interpretation of the study's results? Representativeness could be an issue in the findings of the study especially when not applied to larger population outside the study population. Also this could lead to sampling or selection bias. Question 9: From this table, calculate the proportion of cases and controls who smoked. Proportion of cases who smoked: 1350/1357=.99 Proportion of controls who did not smoke: 1296/1357=.96 Cigarette smoker Cases Controls 1350 1296 Non-smoker 7 61 Total 1357 1357 1350/1357 = 0.995 0.9550 Proportion Smoked 99.5% 95.5% Question 10: What do you infer from these proportions? The proportions for both cases and controls is very close and appear to be same. Question 11a: Calculate the odds of smoking among the cases. Odds ratio= [(1,350 * 61) /(1,296 *7)]=82350/9072=9.1 Question 11b: Calculate the odds of smoking among the controls. Odds ratio of smoking among controls is 99% Odds ratio of smoking among control =(1,296* 7) /(1,350*61) =0.1 or 99% Cases Controls Cigarette smoker 1350 1296 Non-smoker 7 61 Total 1357 1357 Question 12: Calculate the ratio of these odds. How does this compare with the cross-product ratio? Comparing the ratio of these odds is 9.1 and it was compare with the cross ratio by exposure to smoking which shows that risk of smoking also has effects on other health condition. Cases Controls Cigarette smoker 1350 1296 Non-smoker 7 61 Total 1357 1357 1350/1357 = 0.995 0.9550 Proportion Smoked = 99.5% 95.5% smokers/non-smokers 192.9 21.2 Odds 192.9/1 21.2/1 (smokers/non- 9.1 smokers)cases]/(smokers/nonsmokers)(controls) Odds Ratio (OR) 9.1 Question 13: What do you infer from the odds ratio about the relationship between smoking and lung cancer? The Odds Ratio (OR) is 9.1, which means smoking increases the risk for lung cancer, and individuals who smoke are 9 times more likely to develop lung cancer than individuals who do not smoke. Question 14: Compute the odds ratio by category of daily cigarette consumption, comparing each smoking category to nonsmokers. Daily Number of Cigarettes Number of Cases Number of Controls Odds Ratio smokers (cases) * non-smokers (controls) A smokers (controls) * non-smokers (cases) B A/B 0 7 61 - - - - 1-14 565 706 (565*61)/(7*706)= 7.0 34465 4942 7.0 15-24 445 408 (445*61)/(408*7) =9.5 27145 2856 9.5 25+ 340 182 (340*61)/182*7)= 16.3 20740 1274 16.3 All smokers 1350 1296 (1350*61)/(1296*7)= 9.1 82350 9072 9.1 The Odds Ratio for 1-14 cigarettes equal to 7.0 The Odds Ratio for 15-24 cigarettes is 9.5 The Odds Ratio for 25+ cigarettes is 16.3 The Odds Ratio for all smokers is 9.1. Question 15: Interpret these results. These results can be interpreted as cigarette smoking is a risk factor for lung cancer and that the odds of developing lung cancer increases with the number of cigarettes a person smokes on daily basis. Question 16: What are the other possible explanations for the apparent association? There could mean there is a correlation between number of cigarette smoked and lung cancer, but that does not mean smoking cause lung cancer. It could also mean a bias selection, a confounding or error in information collected. Question 17: How might the response rate of 68% affect the study's results? This response rate of 68 percent could suggest there is selection bias in the study. Question 18: Compute lung cancer mortality rates, rate ratios, and rate differences for each smoking category. What do each of these measures mean? These results can be interpreted the rates of mortality rates increase as the daily number of cigarettes a person smokes increase. Daily Number of Cigarettes Deaths Person-years at Risk Mortality Rate per 1,000 person-years Rate Ratio Rate difference per 1000 personyears 0 3 42800 0.07 8.10 0.50 1-14 22 38600 0.57 19.80 1.32 15-24 54 38900 1.39 32.40 2.20 25+ 57 25100 2.25 18.60 1.23 smokers 133 102600 1.30 Total 136 145400 0.94 Question 19: What proportion of lung cancer deaths among all smokers can be attributed to smoking? What is this proportion called? The proportion of lung cancer deaths among all smokers can be attributed to smoking is 94.6%. This proportion is called Absolute Risk. Question 20: If no one had smoked, how many deaths from lung cancer would have been averted? Based on the proportion rate lung cancer about 95 percent of deaths can be attributed to smoking. If no one had ever smoked, 133 from lung cancer would have been averted. Question 21: Which cause of death has a stronger association with smoking? Why? Lung cancer have a stronger association with smoking. The rate ratio for lung cancer is at 18.5, whereas the rate ratio for cardiovascular disease is at 1.3. This could mean that there is higher association between lung cancer and smoking, than it is cardiovascular disease and smoking. Question 22: Calculate the population attributable risk percent for lung cancer mortality and for cardiovascular disease mortality. How do they compare? How do they differ from the attributable risk percent? Smokers Non-smokers ALL Rate Ratio Excess deaths per 1000 personyears Attributable risk percent among smokers Lung Cancer 1.3 0.07 0.94 18.5 1.23 95% Cardiovascul ar Disease 9.5 7.32 8.87 1.3 2.19 23% Population attributable risk percent for Lung cancer disease =(0.94-0.07)/(0.94)*100= 92.5 about 93% Population attributable risk percent for cardiovascular disease (8.87-7.32)/8.87*100= 17.4% Both percentage show death for lung cancer and cardiovascular disease can be attributed to smoking. However, the population attributable risk percent for lung disease (93%) is much higher than the population attributable risk percent of cardiovascular disease (17.4%) this could mean that individual who smoke can have higher risk factor of lung disease and it could be that there is association between lung cancer and smoking. Question 23: How many lung cancer deaths per 1,000 persons per year are attributable to smoking among the entire population? How many cardiovascular disease deaths? Lung Cancer: 0.87 deaths per 1,000 person-years Lung Cancer Death =(0.94-0.07)= 0.87 Cardiovascular Disease: 1.54 deaths per 1.000 person-years Cardiovascular Disease= (8.87-7.32) Question 24: What do these data imply for the practice of public health and preventive medicine? The data implies that smokers are at highest risk group for lung cancer compare to the group who never smoke. Also quitting smoking reduces the risk/mortality rate for lung cancer. Public health intervention/education such as smoking cessation for individual who smoke will most likely to reduce mortality rate for lung cancer. Question 25: Compare the results of the two studies. Comment on the similarities and differences in the computed measures of association Both studies show the association between deaths of lung cancer and how is link to smoking. Both studies also show how the risk factor of cigarettes smoking increased the risk of a lung cancer. The differences is that rates ratios for the cohort study presents strong evidence then the odds ratios in the case-control study. Question 26: What are the advantages and disadvantages of case-control vs. cohort studies? Advantages/disadvantages Sample size/cost Study time Case-control – Case-control – Cohort Cohort disadvantages advantages Disadvantages Advantages Smaller size Cost-effective expensive Larger inexpensive lengthy- takes quick results long time to conduct it Rare disease Not good for rare Good for Not good Good Rare exposure exposure studying rare looking at looking at Multiple exposures Not good looking diseases studying rare rare at multiple Good looking diseases exposure outcomes at multiple not good Good exposures – looking at looking at multiple multiple exposures outcomes - Good Multiple outcomes Progression, Not good looking - spectrum of illness at spectrum of looking at Disease rates illness spectrum of Not good looking illness at rates of the Good disease looking at rates of the disease Recall bias Has potential for - - Has bias less/minimi zes recall bias Loss to follow-up Has selection bias Selection bias less potential potential for Has less for loss to loss selection follow up bias Question 27: Which type of study (cohort or case-control) would you have done first? Why? Why do a second study? Why do the other type of study? I would have conducted a case-control study because case control can be used when etiology of the disease and the information about the disease is available. Case control also is cost effective and easy to complete, especially for this particular study if we want to know association between lung cancer and cigarette smoking. Question 28: Which of the following criteria for causality are met by the evidence presented from these two studies? YES Strong association= YES Consistency among studies= YES Exposure precedes disease= YES Dose-response effect= Biologic plausibility = NO YES NO Reference Friis R.H. and Sellers T. A. (2014) Epidemiology for Public Health Practice, 5th ed.. Jones and Bartlett