Allison Erickson

Case Study: Cigarette Smoking and Lung Cancer

1. What makes the first study a case-control study?

The first study was a case-control study because Doll and Hill studied individuals with the disease who were smokers (cases) and individuals who were smokers with a different disease diagnosis (controls). Also, the unit of observation in this study was the individual with one observation point.

2. What makes the second study a cohort study?

The second study was a cohort study because the unit of observation was a group of data obtained from a secondary source before investigators sent questionnaires. Also, the information obtained about smoking behaviors was obtained from multiple sources and times.

3. Why might hospitals have been chosen as the setting for this study?In a case-control study, there should be one observation point. Given that the disease of

interest was regarding cancer, the most appropriate place for observation would be hospital where the sick go for treatment.

4. What other sources of cases and controls might have been use?Another source that could have been used for this case-control study could have been

an elder care or nursing home facility. Now, I am not saying that only older adults are diagnosed with lung cancer, but because lung cancer can be the result of long years of smoking, doing a similar study in this type of facility may be beneficial. I would say that the same technique could be used in terms of having cases be lung cancer patients who are, or have been, smokers, compared to smokers with other health disease diagnosis.

5. What are the advantages of selecting controls from the same hospital as cases?The advantages of selecting controls from the same hospital include have a consistent

form of care received, treatment options being similar, and knowledge about the patients from a medical staff that works together. Similarly, health records would be in the same location creating less need for searching elsewhere for information.

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6. How representative of all persons with lung cancer are hospitalized patients with lung cancer?

This is not fully representative because there are many stages of lung cancer. I would presume that the only patients hospitalized are those in later stages of cancer, close to death. Therefore, for many of the lung cancer patients in the hospital do not accurately represent all cases of lung cancer present in a given community.

7. How representative of the general population without lung cancer are hospitalized patients without lung cancer?

This representation would be even less than those with lung cancer not hospitalized. With a vast amount of medical diagnosis and concerns in which people go to the doctor for, it would still not be a good representation of the general population. However, if there are more people hospitalized for something other than lung cancer, which may lead investigators to another environmental or social health concern that would need attention.

8. How may these representativeness issues affect interpretation of the study results?

The representativeness issues could affect the interpretation of the study results by giving a false or inaccurate sense of a true health problem. In essence, the results could be skewed to represent smoking to not be attributed to lung cancer based on the number of patients hospitalized with lung cancer. On the other hand, if a lot of smokers are admitted for other health concerns, then that would open the door for additional research not related to lung cancer and smoking.

9. From this table, calculate the proportion of cases and controls who smoked.

Proportion smoked, cases: 51.0%

Proportion smoked, controls: 49.0%

10. What do you infer from these proportions?The inferences that can be made from the proportions is that smoking results in many

other health concerns besides just lung cancer.

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11.a. Calculate the odds of smoking among the cases.

99.5%

b. Calculate the odds of smoking among the controls.

95.5%

12. Calculate the ratio of these odds. How does this compare with the cross-product ratio?9.08. This compares by showing that the exposure to smoking was high for both the

cases and the controls. In addition, this indicates that the risk of smoking affects other areas of health diagnosis, as well as lung cancer.

13. What do you infer from the odds ratio about the relationship between smoking and lung cancer?

The odds ratio allows me to infer that there is a strong and significant relationship between smoking and lung cancer.

14. Compute the odds ratio by category of daily cigarette consumption, comparing each smoking category to nonsmokers.

Daily Number of Cigarettes # Cases # Controls Odds Ratio

0 7 61 Referent

1-14 565 706 6.97

15-24 445 408 9.50

25+ 340 182 16.3

15. Interpret these results. Although the number of cases and controls decreased as number of cigarettes

increased, the odds ratios indicated a stronger association between lung cancer, or other health concerns, and more cigarettes smoked per day.

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16. What are the other possible explanations for the apparent association?Another possible explanation of the apparent association could be that the study results

came from a hospital where people are ill and seeking treatment. Yes, there is a clear association between smoking and lung cancer; however, there could be other factors for the result of illness or disease. Many times with one lifestyle behavior aiding in the ill-diagnosis, there are usually other environmental, social, or behavioral factors that aid as well.

17. How might the response rate of 68% affect the study’s results?This response rate could provide fairly significant results about associations between

smoking and health concerns because it is over 50%. However, it may limit the clear conclusions the investigators can make in regards to a large population. Nevertheless, having a response rate of 68% is strong to help formulate conclusive evidence about smoking and disease development.

18. Compute lung cancer mortality rates, rate ratios, and rate differences for each smoking category. What do each of these measures mean?

(Please refer to attached table from case study at the end of the document for computed numbers.) First, the mortality rate indicates how many individuals died from lung cancer who smoked and who did not smoke. Secondly, the rate ratio gives an indication regarding how an exposure impacts the risk of the disease. In the case of the smokers who smoke 15 to 24 cigarettes per day, for example, the rate ratio indicates that they have a high risk of developing lung cancer. Lastly, the rate difference indicates the disease burden in the two groups (lung cancer death and no death). The rate difference gives representation of the incidence rate of a particular disease with an exposure as a component cause.

19. What proportion of lung cancer deaths among all smokers can be attributed to smoking? What is this proportion called?

9.77 --- known as a cause-specific rate

20. If no one had smoked, how many deaths from lung cancer would have been averted?133 given that in the study only 136 of the people who died from lung cancer reported

number of cigarettes smoked per day and 3 of the individuals who died from lung cancer did not smoke.

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21. Which cause of death has a stronger association with smoking? Why?Lung cancer death has a stronger association with smoking because the rate ratio

indicates a high risk of developing lung cancer from smoking. Also, although the number of deaths from smoking for cardiovascular disease is high, the number of deaths from cardiovascular disease in nonsmokers is also high.

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?

Lung Cancer = 92.6%Cardiovascular Disease = 17.5%

These results indicate that there is a substantial amount of evidence that smoking clearly contributes to lung cancer mortality. Although smoking can lead to death from cardiovascular disease, there are other factors that also contribute greatly to that disease. With this PAR percentage for lung cancer, it would prompt community intervention to reduce smoking. Compared to the attributable risk percent, these numbers provide information about the population as a whole, both smokers and nonsmokers.

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 = .87 per 1,000 personsCardiovascular Disease = 1.55 per 1,000

24. What do these data imply for the practice of public health and preventative medicine?This data implies that quitting smoking for just less than five years greatly reduces the

risk for developing and dying from lung cancer. Even though there are individuals who have still died from lung cancer after 20 plus years being smoke-free, the rate ratio indicates it is much lower than current smokers. In regards to public health practice, health officials can put into place programming for nonsmokers to avoid picking up a cigarette, especially in younger aged individuals. Quitting smoking will, no doubt, help health outcomes, but abstaining from smoking all together will reduce the risk of lung cancer greatly.

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25. Compare the results of the two studies. Comment on the similarities and differences in the computed measures of association.

Both studies indicate that there is risk in developing lung cancer from smoking. In both studies, the rate ratio and odds ratio for cigarettes smoked 0 to 14 per day are similar. However, once the cigarette use increases the rate ratio and odds ratio start become less similar. In the cohort study the rate ratio clearly gives strong association between lung cancer death and smoking. The case-control study gives a similar result in that the exposure of smoking is a major risk factor for developing lung cancer.

26. What are the advantages and disadvantages of case-control vs. cohort studies?

Case-Control Cohort

Sample SizeA: Smaller, can gather results in a timely mannerD: May not fully represent a population

A: Can give a more accurate picture of exposure and disease riskD: Difficult to gather a large amount of people

CostsA: more cost effective with less participant

D: Can be expensive, requiring grants sometimes

Study TimeA: One observation point, which requires less timeD: may not report on all risk factors prior to the study

A: Provides a more accurate picture of risk and disease associationD: takes a long time

Rare diseaseA: Can be small enough to gather quality information about a rare disease

D: If it’s rare, then the participation would not be high enough for cohort

Rare exposureD: It would be difficult to get both cases and controls

A: Able to gather a large group of people to observe regarding the rare exposure

Multiple exposuresA: With both cases and controls, there will be availability of evaluation multiple exposures at the one observation point

D: With many points of evaluation, it would be more time consuming to have more than one exposure being studied

Multiple outcomesD: With a small sample size, there would be no indication of a risk factor

A: Ability to recognize where the outcomes occurred and make inferences of when they occurred

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Progression, spectrum of illnessD: one point of observation A: multiple points of observation

Disease RatesAre not measured in case-control studies

A: disease rates take into account data from multiple observation points

Recall BiasD: can be a problem because case-controls do not measure past exposure

D: can be a problem, but not as much as for a case-control study because the investigator can potentially use some of that information for the results

Loss to follow-upA: not much of a problem due to no real follow-up for the study outcomesD: can lead to skewed results especially for a pharmaceutical drug

D: Because follow-up is a large part of cohort studies, therefore this can lead to skewed results

Selection biasD: can provide differential results based on who was selected

A: can be a little less of a problem, but should still be avoided for clear results

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 done a case-control study first because it is more efficient and cost-effective. If the first case-control study yielded a significant relationship between an exposure and disease, then I would perform a second study to validate the results further. The purpose of doing a cohort study would be to confirm results of a smaller case-control study over a larger population of individuals or groups of people. Also, it would be advantageous to do a cohort study after a case-control study to evaluate disease rates.

28. Which of the following criteria for causality are met by the evidence presented from these two studies?

Strong Association - MetConsistency among studies - MetExposure precedes disease - MetDose-response effect - MetBiologic plausibility – Not met

Allison Erickson

Computations

Allison Erickson

Allison Erickson

Allison Erickson

Allison Erickson

Allison Erickson