Q1 In a cohort study of 100,000 participants after 10 years follow up 2000 people developed disease A. In the baseline it was found that 10,000 people followed a high saturated fat diet; of these 1500 developed disease A.
a. Draw a two way table (2X2) to present these findings
It is OK to show only this or to complete all cells- this is the information you need to do your calculations
b. Calculate the incidence of disease in the exposed and in the unexposed
c. What is theassociation between the exposure and the disease? Interpret (explain) what this means
d. Calculate the Attributable Risk Fraction
e. Interpret your findings in words
f. Calculate from this data the Population Attributable Risk (PAR)?
g. Interpret your finding
Q2. In a case control study investigating the relationship between the number of common melanocytic naeivi (exposure) and melanoma (outcome) were investigated and were summarised as follow:
|
Number of melanocytic naeivi
|
Melanoma
|
No Melanoma
|
|
> 50
|
139
|
38
|
|
0 - 50
|
357
|
438
|
|
|
496
|
476
|
a. Calculate the appropriate measure of association for this study design and interpret in words
b. Calculate the attributable fraction
c. Interpret the finding
d. Calculate population attributable fraction
e. Interpret your findings and discuss the assumptions necessary for respective interpretation.
Validity - biases in epidemiological studies (short explanation no more than 50 words)
Q3. In a study to determine the incidence of chronic disease, 150 people were examined at the end of the follow-up period. Twelves cases were found, giving a cumulative incidence rate of 8% (check if my calculation is correct). Fifty other members of the initial cohort could not be examined, 20 of them because they died.
a. What source of bias should be of concern in this example
b. What will be the incidence rate if all people who were lost to be followed had the disease and what will be the incidence rate if all people who were lost to be followed did not have the disease. (Show your denominator and numerator in the calculation
c. Based on these calculations, do you think the 8% incidence rate is valid (i.e., accurate) Why yes or why not?
Q4. What bias would you suspect in a survey of the prevalence of depression in the elderly population of a city, based on selecting random sample of members listed in several seniors clubs in the city? Explain and how it will affect your estimate.
Q5. You conduct a randomized controlled trial with vitamin B-12 and placebo and their effect on depressive symptoms. Yourandomly allocated in a double blind study to two groups recruiting from GPs. Thedifference in depressive symptoms between the two groups after 1 year of treatment was notstatistically different but you find out that 30% of women were noncompliant withthe vitamin B-12 tablets. If you omit them from the analysis the results of the study were significant.
What analysis was done first and what was done second - what would you use and why?
Q6. 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
Q7. In a study of maternal use of hormones during pregnancy and increased risk of childhood cancer, it was suggested that women who used hormones during pregnancy would deny this use due to concern that this may have caused their child's cancer.
a. What possible bias it can introduce? (explain briefly)
b. In the same study, it was also observed that mothers who used hormones during their pregnancies were more likely to have had a history of medically complicated pregnancies. Further, and independent of the use of hormones, a history of medically complicated pregnancies may be associated with a subsequent increased risk of several conditions in the children, including cancer. If so, this would be an example of:
i) The role of chance.
ii) Non-differential (random) misclassification.
iii) Recall bias.
iv) Confounding.
c. Explain your choice