Introduction to Epidemiology Assignment 2

The University of Western Sydney
School of Science and Health
Introduction to Epidemiology (401076)
ASSIGNMENT 2
SCCS2, 2019

Question 1: [24]
Read the following paper, and answer the questions below:
“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.”
(a) “What study design does this study employ?” [2 mark]
The study employs a national population based case-control study design. By
contacting the families of newborn infants referred for a surgical treatment of cleft
and born between 1996 and 2001 in Norway, the data collected acted as the sample
for the research. The controls were chosen by selecting about four in every thousand
live births
(b) “What justification do the authors provide for conducting this study?” [2
marks]
The authors argue that although revelation that folic acid in early pregnancy
decreases the chances of neutral tube defects is a vital discovery in the field of health,
previous studies relating folic acid in early pregnancy and facial clefts in humans have
offered conflicting results. Accordingly, the authors intent to address these
inconsistencies by investigated the possible impact of folic acid on facial clefts.

(c) “Can the same research question could be explored in Randomised
Controlled trial, explain why yes or why not?” [4 marks]
In a Randomised Control trial, the subjects are randonly selected and
randomly allocated to experimental group that is subjected to intervention, and control
group that is subjected to alternative or conventional treatment (Kendall, 2003). Given
that the subjects in the study are not subjected to treatment by researchers, it is
technically ineffective to use RCT. Because outcome (of folic acid) being investigated
is already known, researchers have to ensure that the ‘experimental group’ includes
newborn infants with clefts hence deviating from RCT that entirely relies on random
assignment. However, if the question was to be addressed by following a cohort of
pregnant mothers (from inception) then randomly dividing them into groups; with one
being supplemented with folic acid and the other being excluded for folic acid then
cases of clefts assessed, RCT would be applicable. Even so, it would be unethical to
risk the health of infants for research.
(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.” [4 mark]
The overall crude OR in consuming ≥400μg of folic acid per day was 0.66 while
adjusted OR stood at 0.61 (in consuming ≥400μg of folic acid per day). In case of no
consumption of folic acid, the overall crude OR was 0.77 while the adjusted OR was
0.75.
(e) “How would you interpret the finding in 4 (d)?” [4 marks]

The findings of the study indicate that when folic acid supplements are taken
during early pregnancy, the chances of isolated cleft lip are decreased by about
33.33%. However, the contribution of other vitamins and dietary factors enhance the
outcome. Additionally, negative lifestyle factors such as smoking or drinking alcohol
increases the risk of isolated cleft lip.
(f) “The authors state that the controls in this study are population-based
controls - are they? Why or why not?” [4 marks]
According to Connally, et al. (2013), population-based case-control study are
slected from an absolutely defined population. The definition may be on the basis of a
geographical area or a population that share certain characteristic such as a disease.
The controls are subsequently selected from the same population hence referred to as
population-based controls. Therefore, in this study, referring to the controls as
population-based controls is incorrect. Whereas subjects investigated were collected
by contacting families of all newborn infants (1996 to 2001) that were referred for
surgical treatment of clefts, the controls were selected from medical birth registry of
Norway on a random basis.
(g) “What could be the source of measurement bias in this study and did the
authors tried to alleviate this problem. Explain with evidence from the text.” [4
marks]
One of the sources of bias in the study in recall errors. Recall bias emanates
from the inability of participants to precisely or completely past events inquired by a