Introduction to Epidemiology

This document provides an introduction to epidemiology, focusing on a study that assesses the risk of cleft lip with or without cleft palate and the association with folic acid supplements. It includes questions and answers about study design, research justification, interpretation of findings, and potential biases. The document also discusses the association between smoking and cleft lip, as well as the association between diabetes and atrial fibrillation stratified by sex. Finally, it explores the possible biases introduced by maternal use of hormones during pregnancy.

Running head: PUBLIC HEALTH 1
Introduction to Epidemiology
By (Name of Student)
(Institutional Affiliation)
(Date of Submission)

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Question 1: [24]
(a) “What study design does this study employ?” [2 mark]
This study employs epidemiological study design. This is because the researchers are
much interested in measuring and assessing the relationship of exposure with a
disease or an outcome.
(b) “What justification do the authors provide for conducting this study?” [2 marks]
The authors conducted the study in order to assess the risk of cleft lip with or without
cleft palate which seems to be substantially reduced by folic acid supplements during
the month before pregnancy and the first two months of pregnancy.
(c) “Can the same research question could be explored in Randomised Controlled
trial, explain why yes or why not?” [4 marks]
Yes. The same research question can be explored in randomized controlled trial
because the pregnant mothers can be randomly allocated to receive one of the several
clinical interventions. In most cases, one of the interventions is the standard of
comparison or control which in this case, Norway has been chosen as a control.
(d) “What was the overall crude and adjusted OR of cleft lip with or without cleft
palate in those consuming ≥400μg of folic acid per day compared to no consumption
of folic acid.” [2mark]
The overall odds ratios for clefts with folic acid supplements. The crude odds ratio
with folic acid of ≥400 μg/day was 0.66 (95% confidence interval 0.47 to 0.95) for
cleft lip with or without cleft palate and 0.81 (0.53 to 1.26) for cleft palate only.
(e) “How would you interpret the finding in 4 (d)?” [4 marks]
This implies that the associations were present only among the cases with isolated
clefts. We therefore restricted subsequent analyses to the isolated clefts. Adjustment
for potential confounding factors slightly weakened the association between folic acid

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and cleft lip with or without cleft palate and removed the association entirely for cleft
palate only. Lacking any evidence of an effect of folic acid on cleft palate only (odds
ratio 1.07, 0.56 to 2.03), we focused the remainder of the analysis on cleft lip with or
without cleft palate.
(f) “The authors state that the controls in this study are population-based controls -
are they? Why or why not?” [4 marks]
Yes. This is so because the cases are originating from a precisely defined population
in Norway and the controls are sampled directly from the same population.
(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]
Regarding this study the cases were drawn from a large and well defined population,
with virtually complete ascertainment, a high participation rate (89 percent), and
clinical confirmation of all defects. Although the participation rate was lower for
controls (76 percent), the controls had the advantage of being drawn randomly from
the entire. This is one of the measurement bias in this which the authors did not
alleviate this problem.

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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 2x2 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]
Cleft lip with
palate
Cleft lip without
palate
Control
Smokers 42 42 55
Non-Smokers 72 72 190
Total 114 114 145
b) “Interpret the findings in (a) in your own words.” [2 marks]
By using the data to calculate the association between the smoking and cleft lip with
or without cleft palate, the value of RR is 1.24. This shows a positive value indicating
a stronger association between the smoking and cleft lip with or without cleft palate.

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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.”[2 marks]
Proportion = 0.67. This shows a smaller proportion of the population.
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 sex
Cases of AF Person years (/1,000)
Males
Diabetes 37 2,336
No diabetes 355 26,454
Females
Diabetes 65 3,896
No diabetes 334 37,120
Total
Diabetes 102 6,232
No diabetes 689 63,574

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a) “Use the data in the table to assess the association between diabetes and atrial
fibrillation, stratified by sex.” [ 4 marks]
To assess the degree and level of the association between diabetes and atrial
fibrillation, stratified by sex, we conduct regression analysis to obtained the
required R values and t-values for inferences
By analysing the above data, the value of R is obtained to be 0.684 which is a
better measure hence suggesting stronger relationship/association between
diabetes and atrial fibrillation. Thus, there exist a stronger association between
the two variables under this case study.
b) “After using the statistical software to compute the sex-adjusted rate ratio they
found that the adjusted RR was 1.51
Is sex best characterised as a confounder or an effect measure modifier of the
relationship between diabetes and atrial fibrillation? Explain.” [4 marks]
In this case, sex is an effect measure modifier since it does not influence both the
dependent and the independent variable for which in this scenario, the dependent
variable is atrial fibrillation and independent variable being diabetes. Also, this is so
because the measure of association between the variables changes over values of
some other variables.
c) “What is the attributable risk of diabetes in males?” [4 marks]

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The attributable risk of diabetes in males based on the result is approximately 23.37
percent. This risk is higher as compared to females which is approximately 17.23
percent.
d) “How would you interpret the finding in 3 (c)?” [4 marks]
The finding suggests that males have relatively higher risk of diabetes than females.
The results further suggests that females have controlled mechanisms towards being
diabetic than males.
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]
The use of hormones can as well introduce bias known as recall bias that is based on
an important mechanism by which stress may affect the susceptibility of the disease,
activity and the outcome of various immune related infections and diseases other than
cancer due to usage of hormones by pregnant mothers.
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.

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iii) The same as the true increased risk.”
The correct choice is (ii): An overestimate of the true increased risk. This can be
so since the risk due to hormone usage cannot be assessed and thus can only be
estimated to be increased.
c) 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:
iv) The role of chance.
v) Non-differential (random) misclassification.
vi) Recall bias.
vii) Confounding.”
Answer: This would be an example of (VI) recall bias.
Explain your answer briefly
This is so because in this case, it would be a systematic error that is caused by
differences in the accuracy and completeness of the recollections retried by mothers
using hormones during their periods of pregnancies.

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References
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.”