University of Western Sydney Epidemiology Assignment 2: Public Health

This document presents a comprehensive solution to an epidemiology assignment centered around a case-control study investigating the relationship between folic acid supplements and the risk of facial clefts. The assignment addresses key epidemiological concepts, including study design, the calculation and interpretation of odds ratios, and the assessment of attributable risk. It delves into the potential impact of recall bias and confounding variables, particularly sex, on the study's findings. The solution analyzes data from the provided research paper, interpreting statistical results and discussing the implications of the study's conclusions. The document covers the use of odds ratios, attributable risk, and the significance of recall bias in epidemiological research. Furthermore, the assignment also explores the potential for bias in studies related to hormone use during pregnancy and its impact on child health outcomes, emphasizing the importance of accurate data collection and interpretation in public health research.

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

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Question 1:
a) The infants in Norway that have the orofacial clefts are treated in surgical centres at the
governmental expenses. The surgical centres are situated in Bergen and Oslo. The researchers
contacted families of such new-born infants that were born between the year 1996 to 2001 that
were referred for the surgical treatment of the cleft. During the same year, the researchers have
selected the randomly of the 4000 live births as controls for both the case groups, these babies
were selected with the case: control ratio of about 1:2 for the cleft lip with or without cleft palate.
and the ratio chosen for the cleft palate is 1:4. Father and mothers were sent with informed
consent (Wilcox et al. 2007).
b) Folic acid deficient is associated with the neural tube defects and the it has been known to
cause the facial clefts in rodents. However, it has been seen that the studies that have associations
with the facial clefts is inconsistent and the question still remains. This question mainly relevant
in the countries that have fortified the folic acid in foods. One such country is Norway where the
there is a highest rate of facial cleft in Europe. Due to this the researchers have assessed the
possible effects of facial clefts in Europe and it has been done through the population based
control study (Wilcox et al. 2007).
c) The same research can also be conducted in a randomised controlled Trial because the within
a randomized controlled trial the experiment is aimed towards new treatment testing and is meant
to reduce bias. The people that are participating in the trial are randomly allocated to either the
group that of receiving a standard form of treatment (control) or a group that is receiving the
treatment under investigation. In the study design it has already been highlighted that the babies
are randomly selected in both the control and the investigation group (Wilcox et al. 2007).

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d) The crude odd ratio is 0.66 and the adjusted odds ratio is 0.65.
e) This means that the associations are present with the isolated clefts. This signify the babies
with no other birth defects. While the adjusted ratio signifies that that the presence of the
potential factors weakens the association between the cleft lip with or without palate and folic
acid.
f) The controls are being drawn in a random manner from the entire population of the births. The
reason for such a conduct is because the participation rate was less for the control and this
required random procedure.
g) In all the cases of case control studies, it has bene seen that recall bias is major concern. The
authors have sent the questionnaires to the women after three months of the delivery and this was
further reduced by the specificity of the findings. It is also important to note that the recall bias
will be working among all the women that in the women that took higher doses but also in the
women that took normal doses of folic acid. Moreover, there was no association with the dose of
less than 400 micro grams per day with the clefts and this also highlight the lack of recall bias
(Wilcox et al. 2007).
Question 2:
a)
Cases Control Total
Exposed 42 55 97
Unexposed 72 190 262
Total 114 245 718

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Odds ratio is 2.01
b) To interpret the data, it is important to mention that the value of the odds ratio is 2.01 which is
greater than 1 and it means that the control is better than the intervention.
c) 36.49 is the proportion of the population within which the cleft lip with or without the cleft
palate is potentially preventable.
Question 3:
a) From the above data it can be drawn that 1.58 percent of males and 1.66 percent of females
are having a positive correlation with the diabetes and atrial fibrillation that are stratified by sex.
Therefore, it can be said that that more number of females are at risk in comparison to the
females. While the males are just slight low than the females in the case of atrial cases that are
occurring due to the diabetes. While it can be said that about 1.34 percent of males and 0.89
percent of females that do not have diabetes are still having cases of atrial fibrillation. Therefore,
it can be highlighted that the person that males that do not have any diabetes are still facing
issues of atrial fibrillation. While at the same time, the females with no diabetes are still facing
issues of atrial fibrillation. There is a no stable correlation between the ones that have diabetes
and the ones that do not have diabetes because both the people are having issues of atrial
fibrillation even if the percentage is very low.
b) Sex can be best described as the confounding variable that has the capability of influencing
both the independent and the dependent variable and it causes the false associations. It is
important to mention that the confounder is just a concept and it cannot be defined and described

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as the association and correlations. While it is also important to mention that the confounding
elements have a modifying effect and it modifies the exposure as well as the outcome due to the
fact that the factor is independently associated with the outcome and the exposure. it is often
seen to be producing missing effects and the exposure under the study is given with the mixed
outcome and the effects are found to be having an addition factor and a distortion in the result
take place. It can also be said that the confounding factor falsely impacts the association between
the more commonly used variables and it brings a false association with the outcome and
treatment where there is actually no real association that exists between them.
c)
Cases Controls Total
Exposed 37 2336 2373
Unexposed 355 26454 26809
Total 392 28790 58364
Attributable risk of males is 0.002. The attributable percentage is 0.2 %
d) The attributable percentage is 0.2 percentage and it can be highlighted that 0.2 percentage
denotes the proportion of the population that are exposed to the disease and such groups can be
attributed to be attributed to the exposure. This also means that the disease can be prevented by
eliminating the risk factor. While at the same time the attributable risk is the difference that
exists between the disease rates in the exposed and the unexposed individuals (Gasparrini and
Leone 2014).
Question 4:
a) In a study which assesses the mother use of hormones during their pregnancy and the increase
amount of risk of the cancer. Here, it is important to mention that the mother was asked to deny

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that fact that they have taken the hormones during their pregnancy, it is a major concern as it
might have caused the child cancer. It is important to mention that the denying the truth of taking
hormones during the pregnancy is a major flaw in a study and it lead to serious biasness into the
study. The data will be reflected wrongly and a relationship cannot be maintained when the data
and faked and covered. The mothers that haven actually taken hormones during their pregnancy
will have higher chances of having a baby that will have cancer and it will lead to biased data
and mismatched data representation.
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.
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
It will be a result of recall bias because the even if the mother re seen to be having
difficulties and facing issues with pregnancies if they take hormones. The one that have taken
hormones during the times of pregnancy is surely going to have issues during the time of
pregnancy. Such mother will experience medically complicated pregnancies and it will lead to an
increased amount of risk among the mothers and the children. However, it has also been seen
that independent usage of the hormones can also lead to and medical complexities and it later on
is associated with the increased amount of risks like the cancer and other related issues in mother
as well as the children. Recall bias can be described as the systematic error and in such cases the
participants do not remembers the previous needs and the experiences are measured accurately.

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The volume and the accuracy deals with the large volumes of memory and it is important to
mention that the memories are subsequently by the experiences and the subsequent events.
Therefore, it is a vital point that the recall bias is a problem is studies that are self-reported, like
the retrospective cohort studies, and the case control studies (Althubaiti 2016).

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Reference
Althubaiti, A., 2016. Information bias in health research: definition, pitfalls, and adjustment
methods. Journal of multidisciplinary healthcare, 9, p.211.
Gasparrini, A. and Leone, M., 2014. Attributable risk from distributed lag models. BMC medical
research methodology, 14(1), p.55.
Wilcox, A.J., Lie, R.T., Solvoll, K., Taylor, J., McConnaughey, D.R., Åbyholm, F., Vindenes,
H., Vollset, S.E. and Drevon, C.A., 2007. Folic acid supplements and risk of facial clefts:
national population based case-control study. Bmj, 334(7591), p.464.