This document discusses different types of epidemiological studies, including observational analytical studies like cohort and case-control studies, as well as interventional experimental studies. Cohort studies follow groups over time from exposure to disease outcome, while case-control studies compare cases and controls retrospectively from disease outcome back to exposure. Experimental studies actively manipulate variables to evaluate new drugs, technologies, programs, and more. Both observational and experimental studies have advantages like establishing causality, but also disadvantages like costs or ethical concerns.

1. Observational
Analytical and
Interventional Studies
S U B M I T T E D B Y-
V I K AS AAG R AH AR I
P H AR M - D

2. Observational Analytical studies -
• Cohort study
• Case control study
Experimental studies -
• Clinical and preventive trials
• Pre, quasi and true experimental studies

3. Concept of
cohort
The word cohort is derived from the Latin “cohorts”
meaning an enclosure, company, or crowd. In Roman
times a cohort was a body of 300–600 infantry.
In epidemiological terms the cohort is a group of
people with something in common, usually an
exposure or involvement in a defined population
group.

4. Definitio
n
Cohort study is a type of analytical
study which is undertaken to obtain
additional evidence to refute or support
existence of association between
suspected cause and diseases.
• Other names of cohort study are
Longitudinal study, Incidence study and
forward looking study

5. Features of
cohort
studies
Cohorts are identified prior to
appearance of disease under
investigation
• The study groups are observed over
a period of time to determine the
frequency of disease among them
• The study proceeds from cause to
effects

6. Indications for cohort study
• There is good evidence of an association between exposure and disease,
from other studies.
• Exposure is rare.
• Attrition of study population can be minimized.
• Sufficient fund is available.

7. Consideration
during
selection of
Cohort
• The cohort must
be free from
disease under
study.
• Insofar as the
knowledge permits,
both the groups
should be equally
susceptible to
disease under
study.
• Both the groups
must be
comparable in
respect of all
variable which
influence the
occurrence of
disease
• Diagnostic and
eligibility criteria of
the disease must
be defined
beforehand.

8. Types of cohort study
• Prospective
study
•
Retrospective
cohort study
• Ambi-
directional
cohort study

9. Steps of
Cohort Study
1 -Selection
of study
population
2 -Obtaining
Data on
exposure
3 -Selection
of comparison
group
4 -Follow up
5 -Analysis

10. Advantage of
Cohort
Studies
• Multiple outcomes can be measured for any one exposure.
• Temporality can be established
• Suitable for new/unusual or rare exposures.
• Can measure incidence and prevalence
• Provide direct estimate of risk.
• Less chance of bias.
• Strongest analytical capacity (among analytical studies)

11. Disadvantag
e of Cohort
Studies
• Costly and time consuming.
• Large sample size is required.
• High chances of drop out.
• Prone to confounding.
• Being in the study may alter participant's
behavior.
• Not suitable for a rare disease.
• Classification of individuals (exposure or
outcome status) can be affected by changes in
diagnostic procedures.
• May arise ethical issues.

12. Case Control
Study
A study that compares two groups of people: those with the disease or condition
under study (cases) and a very similar group of people who do not have the disease
or condition (controls).
A case control study involves two populations – cases and controls and has three
distinct features :
• Both exposure and outcome have occurred before the start of the study.
• The study proceeds backwards from effect to cause.
• It uses a control or comparison group to support or refute an inference.
Case : A person in the population or study group identified as having the particular
disease, health disorder or condition under investigation.
Control: Person or persons in a comparison group that differs, in disease
experience (or other health related outcome) in not having the outcome being
studied.

13. Design of
Case Control
Study
The investigator selects cases with the
disease and appropriate controls without
the disease and obtains data regarding
past exposure to possible etiologic factors
in both groups. The investigator then
compares the frequency of exposure of the
two groups.

14. Interventional Studies
Interventional study also called Experimental study Investigators intervene in the natural
history by actively altering one of the variables and then making inference on the relationship
between variables based on the outcomes.

15. Experimental
study can
evaluate
• New drugs and new treatment of
diseases
• New medical and health care technology
• New methods of primary prevention
• New program for screening
• New ways of organizing and delivering
health services
• New community health programs
• New behavioral intervention programs

16. Types
• Pre-experimental: There is
manipulation of variable but does not
have control group.
• Quasi-experimental study: There is
manipulation of certain variable and has
control group but no randomization.
• True experimental design: Three
features: Randomization, manipulation
and control

17. Types of
Trials
Therapeutic (clinical Trial)
• Study population – Patients with disease
• Objectives
– Cure patients
– Prevent recurrence of disease/risk of death
Preventive (community Trial)
• Study Population – Population at risk
• Objectives – Reduce the risk of developing
disease

18. Advantages of Experimental study
◦ 1. Best Results
◦ 2. Determine Cause and Effect
◦ 3. Variables Are Controlled
◦ 4. Easily Replicated
Disadvantages of experimental study
◦ 1. Costly
◦ 2. Methodologically demanding
◦ 3. Not Real Life Situations
◦ 4. Human Errors