University EPIDEMIOLOGY Assignment: Folic Acid and Facial Clefts Study

This assignment analyzes a case-control study investigating the relationship between folic acid supplements and the risk of facial clefts, as well as exploring other health factors. The study design, justification, and the limitations of randomized controlled trials are discussed. The assignment calculates and interprets odds ratios, examines population-based controls, and identifies potential measurement bias. It further analyzes the association between smoking and cleft lip, calculates the strength of association and explores the potential preventability of cleft lip. Additionally, the assignment examines the association between diabetes and atrial fibrillation, stratified by sex, assessing confounding and calculating attributable risk. Finally, the assignment discusses potential biases in a study on maternal hormone use during pregnancy, and identifies confounding factors.

Running head: EPIDEMIOLOGY
Topic: EPIDEMIOLOGY
Name of the Student:
Name of the University:
Author Note:

1EPIDEMIOLOGY
Question 1:
(a) “What study design does this study employ?”
The study design has been well explained by the author. Infants with orofacial clefts have
been treated at governmental expense in the surgical centres. Random selection of the
average of total 4000 births has been done. Controls have also been considered in the study.
(b) “What justification do the authors provide for conducting this study?”
The authors have seen that countries where fortification of foods is done, folic acid has not
been allowed have taken into consideration. The main research question has been addressed
at the highest rates of facial clefts in children in Norway. The link between folic acid
deficiency and neural tube defects lading to orofacial clefts has been found. Thus this link has
been justified by the authors through the findings of the study.
(c) “Can the same research question could be explored in Randomised Controlled trial,
explain why yes or why not?”
Randomised control trails cannot be used in this study.
Randomised control trails are usually addressed with the aspect of trials. These trials improve
endeavour of the generation of the evidence of effectiveness of health interventions. Thus for
the randomised control trials to be incorporated in this qualitative study, there should be
measures taken by the researchers considering it at the pre-trial stage along with being
explicit about the evidence based practice in experiments.
(d) “What was the overall crude and 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.
The folic acid supplementation during pregnancy has been associated with reduced risk of

2EPIDEMIOLOGY
isolated left lip or without cleft palate after multivitamin adjustment. The odds ratio or OR
have been 0.61. The confidence interval has been considered to be 95% from an interval of
0.39 to 0.96.
(e) “How would you interpret the finding in 4 (d)?”
Odds ratio is a measure of comparison which compares the odds of occurrence of diseases
along with those who have been exposed to the disease than those who have not been
exposed. Thus form the given calculation of the odds ratio the presence of association of
cleft along with the deficiency of the folic acid measured by 400 g supplement has been
calculated.
(f) “The authors state that the controls in this study are population-based controls - are they?
Why or why not?”
Population based controls are those where vases usually come from a defined population and
a fixed geographical area and controls are sampled mainly form the same population. This
study is population based as only the infants born in the time period of 1996 to 2001 among
only the residents of Norway have been considered. Thus the population has been fixed to a
time period and only the state of Norway has been chosen.
(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.”
There has been source of measurement bias as the errors in the analysis have occurred
randomly without favouring a bias. Evidence from the text is “We cannot reconstruct the

3EPIDEMIOLOGY
mothers′ complete exposure history retrospectively, but the collection of brands, bottles, and
labels allowed us to correct some errors in self-report.”
Facial cleft lip ( with or without cleft
palate)
Control
Smokers 42 55
Non smokers 72 190
Question 2
“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.”
The strength of association from the given data relating to the presence of facial clefts among
smokers or non-smokers has been listed in the above table.
b) “Interpret the findings in (a) in your own words.”
From the above table the strength of association between the variables can be determined.
Here the probability of having an oral cleft have smokers and non-smokers has been

4EPIDEMIOLOGY
determined as well as compared with a control group.
The strength of the relationship of oral cleft with smoking can be determined here as weak or
strong. The difference between the presence of cleft among non-smokers have been evident
form the gap between the experimental and control groups. Thus there have been a total of 42
smokers and 72 non-smokers who have shown to have a facial lift (Liu et al., 2015).
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.” explain in words
your findings
The population under the crude risk ratio of 0.97 among the intake of less than 400 gm of
folic acid supplements have been considered to be preventable as they have the greatest
chances of being saved from having a cleft.
Question 3:
“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

5EPIDEMIOLOGY
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
a) “Use the data in the table to assess the association between diabetes and atrial fibrillation,
stratified by sex.”
Males Females

6EPIDEMIOLOGY
Diabetes 37 65
No diabetes 355 334
It means that almost 35 males have the chance of having diabetes and similarly 65 women
have the chance of suffering from diabetes. Similarly, both 355 and 334 men and women
respectively have no changes of suffering from the disease. The strength of association
between the variables and the causal factors is seen here where the number of men and
women are variable and the risk of getting diabetes is the causal factor.
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.”
An increased risk ratio is an indication of higher chance of association between the two
variables that is diabetes and atrial fibrillation. Thus the chance of a confounding and
modification relationship has been found to be moderate than other variables. Sex can
described as an a confounder between the association of diabetes with atrial fibrillation.

7EPIDEMIOLOGY
c) “What is the attributable risk of diabetes in males?”
Attributable risk is the difference between disease rates between exposed and unexposed
variables.
Formula for attributable risk is a/a+b –c/c+d
= (37/37+355)- (65/65+334)
=0.11
d) “How would you interpret the finding in 3 (c)?”
From the following study it can be understood that the percentage or proportion of the
diseases which can be attributed to the exposable risk of suffering from diabetes is 0.11. That
is there is a 0.11 change of being affected with the disease .
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)”

8EPIDEMIOLOGY
Biasness is termed as the fluctuation of the actual results in a study due to the introduction of
a new component or a factor changing the statistical parameters. Here the incorporation of
hormones in the study would change the course of results causing a new of developing the
risk of the diseases thus causing biasness.
b) “If so, an effect of this kind would be likely to result in an observed relative risk which is:
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.”
Since observed relative risk is the same as absolute risk it is a reflection of risk associated
with the disease. Thus the observed relative risk would be the same as the true risk. However
in many cases of the relative risk is less than one then it would be an underestimate of the
exposed true risk while the opposite would occur if it is greater than one.
c) “In the same study, it was also observed that s that 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

9EPIDEMIOLOGY
iiii) The role of chance.
v) Non-differential (random) misclassification.
vi) Recall bias.
vii) Confounding.”
Confounding is usually seen in an experimental study where there is no allowance of the
experimenter in the elimination of the plausible explanations regarding an observed
relationship which is between the dependant and independent variables. In this case here the
history of various medically complicated pregnancies have been associated where there might
be an association between the variables. Thus confounding is the best possible option to be
considered here.

10EPIDEMIOLOGY
References
Wilcox, A. J., Lie, R. T., Solvoll, K., Taylor, J., McConnaughey, D. R., Åbyholm, F., ... &
Drevon, C. A. (2007). Folic acid supplements and risk of facial clefts: national population
based case-control study. Bmj, 334(7591), 464.