Folic acid supplements and risk of facial clefts

Question 1: [24]
Read the following paper, and answer the questions below:
“Wilcox AJ, Lie RT, Solvoll K, Taylor J, McConnaughey DR, Abyholm F, et al. Folic acid supplements and risk of facial clefts: national population based case-control study. BMJ 2007;334(7591):464.”
(a) “What study design does this study employ?” [2 mark]
(b) “What justification do the authors provide for conducting this study?” [2 marks]
(c) “Can the same research question could be explored in Randomised Controlled trial, explain why yes or why not?” [4 marks]
(d) “What was the overall crude and adjusted OR of cleft lip with or without cleft palate in those consuming ?400?g of folic acid per day compared to no consumption of folic acid.” [4 mark]
(e) “How would you interpret the finding in 4 (d)?” [4 marks]
(f) “The authors state that the controls in this study are population-based controls – are they? Why or why not?” [4 marks]
(g) “What could be source of measurement bias in this study and did the authors tried to alleviate this problem. Explain with evidence from the text.” [4 marks]
Question 2 [10]
“In another case –control study researchers investigated cleft lip with or without cleft palate by smoking status in those participants who reported consuming folic acid supplements. In this sub-group there were 42 cases of cleft lip with or without cleft palate and 55 controls who were current smokers; and there were 72 cases of cleft lip with or without cleft palate and 190 controls who were non-smokers.”
(a) “Construct a 2×2 table with columns and rows headings and calculate an appropriate measure of the strength of association between smoking and cleft lip with or without cleft palate in those who consumed folic acid supplements during pregnancy.” [4 marks]
b) “Interpret the findings in (a) in your own words.” [2 marks]
c) “What proportion of cleft lip with or without cleft palate in the population is potentially preventable, assuming a causal association between smoking and cleft lip.”[4 marks] explain in words your findings
Question 3: [16]
“Diabetes is a risk factor for atrial fibrillation. In one study researchers investigated the association between diabetes and atrial fibrillation, stratified by sex. These data are given in the table below.”
Table: Incidence of Atrial Fibrillation (AF) by diabetes status, stratified by sexCases of AFPerson years (/1,000)Males
Diabetes372,336No diabetes35526,454
Females
Diabetes653,896No diabetes33437,120
Total
Diabetes1026,232No diabetes68963,574
a) “Use the data in the table to assess the association between diabetes and atrial fibrillation, stratified by sex.” [ 4 marks]
b) “After using the statistical software to compute the sex-adjusted rate ratio they found that the adjusted RR was 1.51Is sex best characterised as a confounder or an effect measure modifier of the relationship between diabetes and atrial fibrillation? Explain.” [ 4 marks]
c) “What is the attributable risk of diabetes in males?” [4 marks]
d) “How would you interpret the finding in 3 (c)?” [4 marks]
Question 4 [10]
“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)” [4 marks]
b) “If so, an effect of this kind would be likely to result in an observed relative risk which is: [2 marks]
i) An underestimate of the true relative risk of hormone use and increased risk of cancer.ii) An overestimate of the true increased risk.iii) The same as the true increased risk.”
c) “In the same study, it was also observed that s 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: [4 marks]
iiii) The role of chance.v) Non-differential (random) misclassification.vi) Recall bias.vii) Confounding.”
Explain your answer briefly

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