Introduction to Epidemiology Assignment -

Assignment should be typed, with adequate space left between questions.

Read the following paper, and answer the questions below:

Sundquist K., Qvist J. Johansson SE., Sundquist J. The long-term effect of physical activity on incidence of coronary heart disease: a 12-year follow-up study Preventive Medicince 2005; 41:219-225

Question 1 -

(a) What study design does this study employ?

(b) What was the data source used to identify first event of Coronary Heart Disease?

(c) Why the authors excluded 1894 participants who rated their general health as "poor"?

(d) What was the crude overall incidence of CHD?

(e) Compared the relative risk of not doing any physical activity to that of "doing at least twice a week" i) low income ii) in all other?

(f) How would you interpret the relative risk in the above question (e)?

(g) Is the relative risk for this study better described as a risk ratio or a rate ratio? Why?

(h) What do you think would be the major confounders that were not considered in this study? To answer this question you need to read about what are the major classical risk factors for CHD?

(i) Why do you think the author could not adjust for these confounders? Hint: think about the way this study was designed?

Question 2 -

Tasmanian researchers conducted a case -control study to investigate the effect of dietary fat intake on melanoma (Skin Cancer). They hypothesised that people whose dietary fat intake is low will be more susceptible to skin cancer. The study compared 500 cases of melanoma with 500 controls. The controls were randomly selected from the state's electoral roll. The researchers categorised the dietary fat intake into three categories High, Moderate and Low. They found that among skin cancer patients 150 were classified at the low and 80 at the high dietary fat intake whereas among control 130 were at the low and 100 were at the high.

a) Build a table to summarise the data above which will help you estimate the association between dietary fat intake and Skin cancer.

b) Calculate the relative risk (RR) of high fat intake versus low fat intake and the RR of medium to high fat intake in relation to the development of melanoma, what type of RR are these and explain in words the meaning of what you found.

c) Calculate the percent attributable risk due to exposure to low-dietary fat intake on Melanoma and explain in one or two sentences the meaning of your findings.

d) Calculated the population attributable risk of low-fat intake on melanoma and explain in words the meaning of such finding.

e) What do you think about the conclusions of the PAR regarding exposure to low fat diet to reduce melanoma? (No more than 3-4 sentences).

Question 3 -

In a small cohort study investigating the effect of a rare exposure (E), the following results were found:

Table 1

A- Is there an association between exposure and disease? Show the way you reached the conclusion.

B- A stratified analysis by Age-groups shows the following:

What is the relative risk (RR) of exposure causing disease in younger adults and what is the RR in older adults?

c- How do you explain this result? (No more than 60 words).

Question 4 -

a) Give one example of typical bias for a cohort study and explain why it creates a bias (no more than 100 words).

b) Give one example of typical bias for a case - control study and explain why it creates a bias (no more than 100 words).

Question 5 -

A cohort study was conducted to examine cigarette smoking and the risk of oral cancer. The investigators selected exposed and unexposed subjects so that they had exactly the same distribution of race. This method to address confounding by race is called:

i. Restriction

ii. Stratification

iii. Matching

iv. Multivariate analysis

v. None of the above

Question 6 -

A study aims to determine the incidence of type 2 diabetes. A cohort of 200 people age 65 years or older who were initially disease -free participated in the study. One hundred and fifty people were examined at the end of 3 years. Fifty other participants from the initial cohort could not be examined, including 11 people who had died. Does this loss of participants represent a source of bias? Justify your answer. No more than 80 words.