Epidemiology Study Analysis: Retrospective Cohort and Clinical Trials

This assignment provides an analysis of two epidemiological studies. The first study is a retrospective cohort study comparing exposed and non-exposed groups to determine the incidence of cancer, highlighting the use of this design for assessing disease associations over lengthy latent periods. The second study investigates the association between Hepatitis C Virus (HCV) and B-cell non-Hodgkin lymphoma (B-NHL), suggesting a clinical experimental study as the most appropriate design. The assignment calculates the relative risk (RR) and odds ratio (OR) to assess the strength of association between HCV exposure and B-NHL occurrence. The RR calculation, based on provided data, indicates no significant association, while the OR is used to estimate the percentage of B-NHL cases among HCV positives that could have been prevented.

Question Two
Analytical studies are essential in providing evaluation of causality of
an association which is capable of estimating the magnitude of the risk
involved. Cases under study are assessed on the disease state and the
exposure which they are involved. Analytical studies fall under two
categories of being either longitudinal or cross sectional studies. Cross
sectional entails exposure and the disease relating to the same period in
time. Longitudinal on the other hand can either be cohort or case control.
Cohort entails identification of individuals with exposure of interest and
section of population which is not exposed. In case control studies, cases
are located and disease patterns are studied for comparing with the
control group. Further cohort studies can either be retrospective or
prospective, or at times other studies uses both approaches. Two or more
groups are studied strictly for diseases association according to their
exposure status, their incidence or mortality traits. Rates of the disease
thus can be studies; however large number of participants must be
studies especially when it comes to environmental exposures. While in
case control studies, the cases or persons of interest and persons not
having the disease are sampled from the general population. Exposures
among cases are often made into comparison among those without the
diseases. Often multiple exposures are assessed and small number of
cases is needed to conclude a precise estimate of risks associated with
the environmental risks involved. When retrospective studies are
conducted.
Thus in the question raised above, a longitudinal study was

conducted among the two groups. Further the study utilised a
retrospective study, where the two groups ; exposed and non exposed
were compared over the same period of time, to determine the incidence
cases of cancer. Thus a retrospective cohort study was used mainly for
these two reasons; the two groups under consideration and the lengthy
latent period under review.
Question Three
a. Experimental studies are epidemiological in nature and often
include clinical trials and population based studies. The nature of these
studies takes into consideration of the varying exposure characteristics. In
this case comparable individuals are assigned randomly to treatment and
intervention group and observed over a specified period of time for any
suspected health outcome of interest. While conducting these studies
ethical concerns must be keenly followed. Further observational studies
can be conducted to assess risks associated with diseases. These are
based on the supportive evidence presented.
In this study in the question, an observation study was conducted the
association of whether having hepatitis C virus influences the risk of B-cell
nonHodgkin lymphomas- BNHL. However the most feasible study design
appropriate for this study is clinical experimental study. The reason to
support this is that, other factors not necessarily having hepatitis C virus
affects of B cell non-Hodgkin lymphoma disease. Further the time frame
for the exposure and other confounding factors need to be measured in
clinical trial and compared to an intervention group to prove causality.

b. Strength of association between HCV AND B-NHL
The common measure of association between exposure and disease
is often calculated in terms of Relative risks or odds ratio. In this study we
shall assess the relative risks of getting B-NHL, when exposed to HCV.
The formula for RR;
= A/(A+B)/C(C+D)
B-NHL patients Non B-NHL patients
Age
(Years)
HCV (-) HCV (+) HCV (-) HCV (+)
 55 163 (A) 18 231(B) 6
> 55 237(C) 52 165(D) 16
= 163/(394) / 237/(402)
= 0.41/0.58
= 0.70
An RR of 0.1 is often indicated as no association between exposure
and diseases occurrence. While decreased risks are often signified by RR
less than 1.0. thus the results indicate that the exposure of HCV is less
likely to increase or decrease the occurrence of B-NHL among the patients
and non patients.
c. Percentage of B-NHL among HCV positives that could
have been prevented
Calculation involved is odds ratio. It is defined as the presence or
absence of a disease which is associated in a given population.
Calculation of odds ratio is meaningful in calculating population that could
have been prevented from the disease. Thus OR signifies an estimation of

RR.
OR = AD/BC
= (163X165)/(231X237)
= 0.49
Percentage that could have been prevented is 0.49x100
= 49% of the HCV positives.