Problems on Epidemiology

This document contains solved problems on epidemiology including cross-sectional study, case-control study, ecology study, risk ratio, odds ratio, quality of life, and side-effects of Prozac.

PROBLEMS ON EPIDEMIOLOGY
The answer to problem 1a
This is a type of cross-sectional study.
Limited/Disability
Residence Type Yes No Total
Rural 344 1036 1380
Urban 444 1519 1963
Total 788 2555 3343
Prevalence in Rural Residence = 344/1380 = 0.2493
Prevalence in Urban Residence = 444/1963 = 0.2262
As shown above, there is an increased prevalence of disability in rural areas compared to
urban areas.
The answer to problem 1b
In this problem, we have to use analytical observation based on the case-control study.
Here those with disability serve as cases and those without disability serve as controls
irrespective of their place of residence (exposure). Case-control studies are used to test
and define a hypothesis.
The answer to problem 2
If we analyze based on the ecology study, as in this case, at an individual level it can be
termed as ecology fallacy. Not only air pollution but also other factors like smoking or
work-related exposures such as asbestos may be having similar or even more adverse
effects on the individual that cannot be explained by maps of population densities or air
pollution.
The answer to problem 3
The risk ratio commonly known as RR is a relative risk ratio comparing risks of two
groups.
Risk ratio = cle / clu
where CIe: cumulative incidence in a group termed 'exposed'
CIu: cumulative incidence in the group termed “unexposed”.
The formula to calculate the risk ratio (RR) and of Cu(CI) using table 1
Treatment Myocardial No Total

Infarction
a
Infarction
b
(a+b) a/(a+b)
Aspirin 139 10,898 11037 0.012594
Placebo 239 10795 11034 0.021660
Total 378 21693 22071
Table 1: data showing myocardial infarction using Aspirin and Placebo
Relative Risk (RR) =0.58
The sampling distribution of the log(RR) is approximately normal with standard
error(SE) calculated as below :
SE(ln(RR))=sqrt [{ EN/{EE(EE+EN)}+ CN/{CE(CE+CN)}}]
Where RR = Relative Risk,EE=Events Experimental CE=Control Events EN=Non
Events Experimental CN=Control Non Events
The 1-alpha confidence interval for the log(RR) is then
CI(1-alpha ) (ln(RR))=ln(RR) ± SE(ln(RR)) * za
Where za is the standard score for the chosen level of significance
SE = Sq[(b/{a(a+b)} + d/{c(c+d)}]
= Sq(10898/139(139+10898) + 10795/239(239+10795)]
=Sq[(10898/139(11037)+10795/239(11034)]
= Sq[(10898/1,534,143 +10795/2,637,126)]
= 7.1036*10-03 + 4.0935*10-03 =0.0112
C.I. =exp[ln(RR) ± 1.96* SE]
= exp[ln(0.58140 ± 1.96*0.0112]
= exp[-0.5423 ± 0.02195]
= exp [-0.5643 to -0.52304]
C.I. = 0.5688 to 0.5920
Interpretation of the result
Interpretation: Physicians exposed to aspirin have a risk that is 0.5814(half) times that
given placebo for myocardial infarction. We are confident of the level 95% of finding the
value for the relative risk varies from 0.5688 to 0.5920. This interval does not have the
value one, making it statistically significant.
The answer to problem 4
Odds Ratio = (53*40/11*58)
= 2120/ 638
= 3.3229 SE

= Sq[(b/a(a+b) + d/c(c+d)]
= Sq(58/53(53+58) + 40/11(11+40)]
= Sq[(58/53(111) +40/11(51)]
= Sq[(58/5883 +40/561)]
= 9.8589*10-03 + 0.07130
=0.0812C.I
. =exp[ln(OR) ± 1.96* SE]
= exp[ln(3.3229) ± 1.96*0.0812]
= exp[1.2008 ± 0.1593]
= exp [1.0415 to 1.3601] C.I
. = 2.8335 to 3.8966
Interpretation: Mothers who had preterm delivery are 3.32 times more likely to be in a
low socioeconomic status compared to those that did not have a preterm delivery. We are
confident (95%) to find this value for the odds ratio to be as low as 2.83 and as high as
3.90. This interval does not have the value one, making it statistically significant.
The answer to problem 5
The ODDs ratio for consumption of alcohol referred to as case 1 (i.e. 50-80
grams per day) is
= (96)(666)/(109)(104) = 5.6401
= 5.64,
suggesting esophageal cancer is 5.64 times more frequent in the exposed group of
the source population.
The ODDs ratio for consumption of alcohol ( i.e. 1-50 g per day) referred to as
Case 2 is
= (85)(666)/(200)(104)
= 2.72
suggesting oesophagal cancer is 2.72 times more frequent in the exposed group of
the source population.
By comparing both the results, oesophagal cancer in case 1 is approximately 2
times that of case 2.It indicates that because of the increase in daily alcohol risk of
being affected by oesophagal cancer increases.
The answer to problem 6a.
Quality of life of persons affected with mental disorder :
A bipolar disorder manifests itself with occasional swings of mood from
depressive lows to manic highs. The exact reason behind this disorder is not yet
fully analyzed but it is a combination of factors like genetically derived or
because of environment issues or altered brain structure.
It has been observed that persons affected with this type of disorder may behave
in both positive and negative ways. Those who are showing a good quality of life

the form of a. feeling sound and controlled b. a positive image c. autonomy d..
engaged in enjoyable and meaningful activities and e. a feeling of optimism.
Poor quality of life because of the negative effect is experienced by those with
serious mental health problems because of a. feelings of distress, b. choice and
autonomy, c. lack of control, d. lack of self-belief and confidence meaning
manifested in the form of a sense of not part of his society; e. diminished activity;
and f. demoralization.
Therefore, while some factors genetic and environmental have strong links with
bipolar disorder, but fewer have enough evidence to prove whether there is any
kind of causality. (Rowland & Marwaha, 2018) The frequency of occurrence of
this disorder cannot be predicted.
The answer to problem 6b
“Cleft lip and cleft palate” are malformations at face and mouth that start
occurring at the initial stage in pregnancy when the baby is at the development
stage inside the mother’s womb. Clefting results because of lack of enough tissue
in the mouth or lip area, and whatever tissue is available does not properly join
together.
Doctors may not always come to know the reason why the baby develops cleft lip
or cleft palate, but many clefts are thought to be because of factors like genetic
(inherited) and environmental (side effects of some medications or deficiency in
vitamins vitamin).There is a possibility either mother or father or both can pass on
genes which may be the cause for developing cleft palate or cleft lip in the baby.
Consuming certain medicines ( some anti-seizure medicines ) during pregnancy
may increase the chance of the mother delivering a baby having cleft lip or palate
problem. Similarly, during pregnancy, if mothers do not get adequate prenatal
nutrients (for example folic acid) may increase the risk of the baby having a cleft.
It is also found out in some cases that mothers who are exposed to certain
chemicals can have the possibility of giving birth to a baby having a cleft.
The answer to problem 6c
The Side-effects for using Prozac include Sexual dysfunction. Stomach upset.
Headaches. Sleep disturbances. Anxiety. Dizziness. Drowsiness, appetite loss etc.
Some scientists have anticipated that if antidepressants of the class of Prozac type
are used on a long term basis, it may lead to a brain tumour.
Prozac-class of antidepressants works by affecting brain serotonin distribution.
This may cause developing and nurturing cancer cells inside the brain leading to
brain cancer. It has been also established in studies that people continue using this
drug can have a suicidal tendency.

References :
Lim, S. S., Vos, T., Flaxman, A. D., Danaei, G., Shibuya, K., Adair-Rohani, H., ... &
Aryee, M. (2012). A comparative risk assessment of burden of disease and injury
attributable to 67 risk factors and risk factor clusters in 21 regions, 1990–2010: a
systematic analysis for the Global Burden of Disease Study 2010. The
lancet, 380(9859), 2224-2260.
Rowland, T., & Marwaha, S. (2018). Epidemiology and risk factors for bipolar
disorder. Therapeutic Advances In Psychopharmacology, 8(9), 251-269. doi:
10.1177/2045125318769235