Introduction to Epidemiology

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

PUBLIC HEALTH 2
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

PUBLIC HEALTH 3
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.