Read​ ​the​ ​article​ ​entitled​ ​“​Intake​ ​of​ ​vitamin​ ​D​ ​and​ ​risk​ ​of​ ​type​ ​1​ ​diabetes:​ ​a birth-cohort​ ​study​”​ ​and​ ​answer​ ​the​ ​following​ ​questions​:

A. What was the main exposure investigated in this study? How was the exposure assessed or determined? Describe how the exposure was treated in the statistical analysis.
B. Using information from Table 1 in the article, calculate and interpret the odds ratio for the association between gender (boys versus girls ) and diabetes (yes versus no). Please show your work including the 2*2 table.
C. In table 2, calculate and interpret the risk ratio for the association of lack of vitamin D supplementation (versus regular) with the risk of type 1 diabetes. Do you think the association would be statistically significant? Why?
D. Is there evidence for a dose-response association of vitamin D supplementation and the risk of type 1 diabetes? Why or why not? Describe this association and justify your answer.

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A. What was the main exposure investigated in this study? How was the exposure assessed or determined? Describe how the exposure was treated in the statistical analysis.
Solution
The main exposure investigated in this study is “Type 1 diabetes”. The exposure was assessed in the first year of life about frequency and dose of vitamin D supplementation and presence of suspected rickets and assessed after December 1997 in children. The effect of exposures on the risk of type 1 diabetes with single and multiple term are analyzed using the Cox proportional hazards. Infant age at the 1–year follow-up visit was included as a covariate in all models that contained growth rate in infancy....