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Question 1. a) What justification do the authors provide for conducting this study?

b) What was the overall adjusted OR of cleft lip with or without cleft palate in those consuming 400g of folic acid per day compared to no consumption of folic acid.c) How would you interpret the finding in 4 (b)?d) The authors state that the controls in this study are population-based controls are they? Why or why not?e) Reflect upon your answer in (d ). The authors could have conveniently recruited controls (those without orofacial clefts but presenting for other reasons) from the surgical centres at the same time as recruiting cases. What might be the effect of using control participants from the surgical centres on the magnitude of the reported OR between folic acid intake and facial clefts? Would the OR move closer or further away from the null value of 1.00? Explain.
Question 2
In a study using the same design as Wilcox et al. 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 22 table 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.

Cleft lip with or without cleft palate

Smoking status
Cases
Controls
TotalCurrent smoker
42
55
97Non-smoker
72
190
262Total
114
245
359

(b) How would you interpret the finding in question 2(a)?

(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?