This document provides an overview of observational study designs, including definition, types, and examples. It discusses cohort studies, case-control studies, and cross-sectional studies. Cohort studies measure events over time to determine causes and prognosis. Case-control studies identify associations by comparing exposures in cases versus controls. Cross-sectional studies analyze a population at a single time point to determine prevalence. Observational studies are useful when randomization is not possible or ethical and can provide faster results than cohort studies.

1. MJP ROHILKHAND UNIVERSITY
DEPARTMENT OF PHARMACY
TOPIC – OVSERVATIONAL STUDY DESIGN
PRESENTED BY – SWATI BAJPAI
M.PHARMA (PHARMACOLOGY)
PRESENTED TO - MRS. NEHA KATIYAR MAM

2. OVERVATIONAL STUDY DESIGN
DEFINITION - Observational studies are called epidemiologic study designs. these
are the only practicable methods of studying various problems.
In observational study, subjects are not randomized to the exposed or unexposed
groups, rather the subjects are observed in order to determine both their
exposure and their outcome status and the exposure status is thus not determined
by the researcher.
Example –
 Studies of etiology
 Instances where the randomized controlled trials might be unethical,
 Or if the condition to be studied is rare.

3. OVERVATIONAL STUDY DESIGN
Types of observational studies
Cohort
Case control
Cross sectional

4. COHORT STUDIES
Cohort studied are used to study -
 Incidences (the number of times disease happens)
 Causes
 Prognosis ( predicting or expected development of a disease, including
whether the sign and symptoms will improve or worsen (and how quickly)
or remain stable over time)
 They measure events in chronological order.
 They can be used to distinguish between cause and effect.

5. Continue :-
 This is a type of observational study in which no intervention (a
treatment, procedure, or other action taken to prevent or treat
disease, or improve health in other ways) for the sake of the study
is done.
 'Prescription event monitoring' is a cohort study.
 'Cohort' is a group of individuals having some common features. In
the context of drug research, the common feature is that all study
subjects have taken a particular drug. Occurrence of events
(beneficial or adverse) in users and nonusers of the drug is
compared.

6. TYPES OF COHORT
STUDIES
1. Prospective cohort
studies
2.Retrospective cohort
studies.

7. 1. Prospective
cohort studies
 A prospective study watches for outcomes, such as
the development of a disease, during the study
period and relates this to other factors such as
suspected risk or protection factors.
 The study usually involves taking a cohort of
subjects and watching them over a long period.
 In which a group of people is chosen who do not
have the outcome of interest,
Example – myocardial infraction.
 The investigator then measures a variety
of variables that might be relevant to the condition.

8. Continue :-
 In the prospective design, all patients who receive the study drug are
followed up for therapeutic outcomes or adverse effects. A matching group
of patients who have not received the drug is identified and followed up to
serve as 'blank'.
 After a time the people in the sample are observed to see whether
they develop the outcome of interest - if they do not develop
the outcomes of interest are used as 'controls' and
another cohort group treated with the agent of interest used as 'treated'.
 Cohort studies are primarily used to discover uncommon adverse effects
that may be missed during formal therapeutic trials which involve fewer
patients and often exclude certain type of patients who may be susceptible
to that adverse effect.

9. Retrospective cohort study
 Retrospective meaning - Looking backward on the past, on what has already
taken place.
 A retrospective study looks backwards and examines exposures to
suspected risk or protection factors in relation to an outcome that is
established at the start of the study.
 In the retrospective cohort study, health records of a population are
scrutinized for exposure to the study drug and the
subsequent beneficial/adverse events.
 These studies used data, already collected for other purposes.
 The study period may be many years but the time to complete the study is
as long as it takes to collect and analyze the data.

10. Population Selected sample
Variable present
Condition
develops
Condition does
not develops
(internal control)
Variable absent
External control
Study design for cohort study

11. Advantages :-
• The use of cohort is often mandatory as a randomized
control trial may be unethical ,Example – we cannot
intentionally expose people to cigarette smoke or asbestos.
Thus research on risk factors relies on cohort studies.
• Single study can examine various outcome variables,
example- cohort studies can simultaneously look at deaths
from lung, cardiovascular, and cerebrovascular disease.
• Incidence can be directly calculated.
• Direct estimation of the relative risk (RR)
• Dose response relationship with exposure can be studied.

12. Disadvantages : -
• The limitations of cohort studies are that controls included may not
be appropriate, and relatively long period of follow up is needed
• They can be very expensive and time consuming.
• They are not good for rare diseases.
• They are not good for diseases with a long latency.
• Differential loss to follow up can introduce bias.

13. CROSS SECTIONAL STUDIES
 Cross-sectional study is a type of observational study that analyzes data
from a population at a specific point in time.
 These studies are used to determine prevalence (proportion of a particular
population found to be affected by a medical condition, typically a disease or
a risk factor such as smoking or seatbelt use at a specific time).
 They are relatively quick and easy but do not permit distinction between
cause and effect.
 Example – the ascending cholangitis in children is very rare enables the
children to look for other causes of abdominal pain in this patient population.

14. Population
Selected
sample
Risk factor
(Disease
present)
Risk factor(No
Disease )
No risk
factor(Disease
present)
No risk factor
(No disease)
Study design for cross sectional studies

15. Advantages :-
 Not costly to perform and does not require a lot
of time.
 Captures a specific point in time.
 Contains multiple variables at the time of the
data snapshot.
 The data can be used for various types of
research.
 Used to prove and/or disprove assumptions.
 Many findings and outcomes can be analyzed to
create new theories/studies or in-depth
research.

16. Disadvantages :-
 Rare conditions cannot be studied using cross
sectional studies because even in a large sample
there may be no one with the disease.
 Cannot be used to analyze behavior over a period to
time.
 Does not help determine cause and effect.
 The timing of the snapshot is not guaranteed to be
representative.
 Findings can be flawed or skewed if there is a conflict
of interest with the funding source
 May face some challenges putting together the
sampling pool based on the variables of the population
being studied.

17. CASE
CONTROL
STUDIES
DEFINITION : -The case–control is a type of epidemiological
observational study.
 Case–control study is used mainly to reveal association of a
suspected rare adverse event with the use of a particular
drug.
Example -(Agranulocytosis caused by phenylbutazone)
 Cases of this suspected adverse event are collected from
hospital records or disease registries.
 Drug histories of both groups are traced backwards to
compare exposure to the indicated drug (e.g. )
among patients with the adverse event to those without it.
 A matched 'control' group similar in other respects but not
having the adverse event is selected.

18. Continue :-
 , the causative drug and the adverse event have to be suspected first to plan the
study, whereas cohort study can reveal unsuspected adverse events

19. Study
individuals
Selected
cases
Exposed Non exposed
Selected
controls
Exposed
Non
exposed
Study design for case-control studies

20. Advantages :-
 Easy to conduct as no follow up is required.
 No attrition, as no follow up is needed.
 Gives faster results.
 Inexpensive.
 Suitable for rare and newly identified diseases.
 More than one risk factors can be studied simultaneously.

21. Disadvantages
v The most commonly cited disadvantage in case-
control studies is the potential for recall bias.
v Recall bias in a case-control study is the increased
likelihood that those with the outcome will recall and
report exposures compared to those without
the outcome.
 he study depends upon the history given by the
subject. Hence recall bias can occur
 Sometimes finding and appropriate control is difficult.
 We can only establish an association between the
disease and the risk factor as we don’t know what
occurred first.
 We can’t know the incidence hence can’t calculate
the relative risk (RR) directly from a case-control
study.

22. Reference
 Essentials of Medical Pharmacology Eighth Edition KD TRIPATHI New Delhi, India.
 Research series Dr. C J Mann, department of Accident and Emergency
medicine, Taunton, Somerset, UK.
 http://www.ihatepsm.com/blog/epidemiology-steps-investigation-epidemic
 http://www.ihatepsm.com/blog/epidemiology-advantages-and-disadvantages-c...
 http://www.ihatepsm.com/blog/epidemiology-advantages-and-disadvantages-c...

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