Public Health Epidemiology STATS HW (Confounding and Effect Modification)

(PROFESSOR’S REMARKS)  For the first Question, I don't know where it came from. If you could, copy it and send it to me. For Q2, the tables are in error and the calculations are incorrect. The answer is as follows: a. Construct the appropriate two by two tables using the data given above. Be sure to label the cells and margins. b. Calculate the appropriate crude ratio measure of association combining the data for young and old individuals. c. Now, perform a stratified analysis and calculate the appropriate stratum-specific ratio measures of association. What are they? d. Do the data provide evidence of effect measure modification on the ratio scale? Justify your answer. a. Total: CHD No CHD Total High Yes 220 9780 10000 Lipid Level No 83 9917 10000 Total 303 19697 20000 Young Old CHD No CHD CHD No CHD High Yes 20 3980 4000 Yes 200 5800 6000 Lipid Level No 18 6982 7000 No 65 2935 3000 38 10962 11000 265 8735 9000 b. Risk Ratio = 2.7 c. Risk Ratios= 2.0 for young people and 1.5 for old people For Question 3, Interviewer bias is the only on avoided.

A. Temporality: This states that the effect must follow the cause, as well if there is delay amongst the cause and effect, then this delay also must show up, i.e. the effect must occur after that delay.

Among the statements mentioned above, the first one provides evidence for temporality: "the main strength in this study involve that the overweight condition was established prior to development of cancer."

B. Biological Gradient or dose-response: This guideline is based on the exposure and its effect. It implies that greater exposure will lead to greater effect. However in some case inverse relation may develop too, i.e. greater exposure leads to lower degree of effect.

The second statement provides the evidence for this guideline, stating that increased BMI (increased exposure) led to increased cancer mortality (increased degree of effect). "The study discovered that morality related to cancer increased at the same rate as BMI increased. Moreover, comparing to normal weight men, the risks for slightly overweight men as well as moderately overweight men and also greatly overweight men were 1.2, 1.3, and 1.5.

C. Consistency: This would be supported by the consistent findings (results) by different studies conducted by different individuals in different place with various samples. This increases the possibility of the effect.

The thirst statement provides evidence for consistency, while asserting that fact that many epidemiological studies (different studies) conducted in US and abroad (different place)

have found similar results (consistent results). "Many epidemiological researches carried out in the United States as well abroad have also discovered that the risk of cancer mortality is mainly increase by high body mass index."

2

Crude ratio for High Lipid level is 0.55 and crude ratio for CHD is 0.15

Hence the High Lipid Level has higher risk within its group and CHD has lower risk within its group.

3

Interviewer bias : No. Since questioners are being mailed. Not an interview.

Exposure misclassification or Information bias is the error arising from measurement error. Yes, it can happen. In fact for different groups of people this error can be different .

Confounding : No . Confounding is a state whereby the effect between an outcome as well as exposure is biased by the occurrence of additional variable. But here , no other variable can affect it. Selection bias : YES. Exposure group to study should be selected randomly. And from every age, sex, financial group , ethnicity the chance of a sample drawn should be equal.

Loss-to-follow-up . Not really. If it's just the 1st time gathering data only , then 'no'.