research design

1. .

2. Study Designs in Epidemiologic
Research
Alam Zeb AmiR
Group members: Wajid Shah , Alam Zeb , Faryal

3. TYPES OF PRIMARY STUDIES
Descriptive studies
 describe occurrence of outcome
Analytic studies
 describe association between
exposure and outcome

4. ANALYTIC STUDIES
Exposure Disease

5. Case report
Case series
Descriptive
Epidemiology
Descriptive
Experimental
Studies
•RCT
•Cross-sectional
study
•Case-Crossover
study
•Case-Control
study
Observational
Studies
•Cohort study
Analytic
•Ecologic study

6. OBSERVATIONAL STUDIES
Case-Control Studies
 an “observational” design comparing
exposures in disease cases vs
healthy controls from same
population
 exposure data collected
retrospectively

7. CASE-CONTROL STUDIES
Cases: Disease
Controls: No disease

8. Study
population
Cases
(disease)
Controls
(no disease)
factor present
factor absent
factor present
factor absent
present
past
time
Study begins here

9. CASE CONTROL STUDY
Unhygienic Food
Unhygienic Food
Hygienic Food
Hygienic Food
Comparison
PresentPast
Colon
Cancer
No
Cancer

10. CASE-CONTROL STUDY
 Strengths
 Less expensive and time consuming
 Efficient for studying rare diseases
 Limitations
 one cannot directly obtain absolute risk of an
outcome
 Exposure measurements taken after disease
occurrence

11. OBSERVATIONAL STUDIES
Cohort Studies
 an “observational” design comparing individuals
with a known risk factor or exposure with others
without the risk factor or exposure
 looking for a difference in the risk (incidence) of
a disease over time
 data usually collected prospectively (some
retrospective)

12. time
Study begins here
Study
population
free of
disease
Factor
present
Factor
absent
disease
no disease
disease
no disease
present
future

13. COHORT STUDY
Smoker
Non-Smoker
Lung Cancer
Lung Cancer
No Lung Cancer
No Lung Cancer
Comparison
Present Future

14. COHORT STUDY
Strengths
 Exposure status determined before disease
detection
 Subjects selected before disease detection
 Can study several outcomes for each exposure
 Limitations
 Expensive and time-consuming
 Inefficient for rare diseases or diseases with long
latency
 Loss to follow-up

15. COMPARISON
Case Control Cohort
Retrospective Prospective/ Longitudinal
Hospital Based Community based
Less time consuming More time consuming
Small sample size Large sample size
Less expensive Very expensive
Rare diseases Common disease
Easy to conduct Difficult to conduct

16. OBSERVATIONAL STUDIES
Cross-sectional studies
 An “observational” design that surveys exposures
and disease status at a single point in time (a cross-
section of the population)
time
Study only exists at this point in time

17. CROSS-SECTIONAL DESIGN
time
Study only exists at this point in time
Study
population
No Disease
Disease
factor present
factor absent
factor present
factor absent

18. CROSS-SECTIONAL STUDIES
 Often used to study conditions that are relatively
frequent with long duration of expression (nonfatal,
chronic conditions)
 Not suitable for studying rare or highly fatal diseases or
a disease with short duration of expression
Disadvantages
 Weakest observational design, (it measures prevalence,
not incidence of disease).
 Usually don’t know when disease occurred

19. EXPERIMENTAL STUDIES
Randomized Controlled Trials (RCTs)
 the “gold standard” of research designs
 a design with subjects randomly assigned to
“treatment” and “comparison” groups
 The subjects in the study who actually receive the
treatment of interest are called the treatment group.
 The subjects in the study who receive no treatment
or a different treatment are called the comparison
group.
o Both groups are followed up for a specified period
o There is a focus on the control of bias

20. time
Study begins here (baseline point)
Study
population
Intervention
Control
outcome
no outcome
outcome
no outcome
baseline
future
RANDOMIZATION

21. A SIMPLE RCT DESIGN
Identified
sample of
subjects
A
B
Treatment group
Control
group/Treatment 2Random
allocation
Parallel Design

22. RCT'S DESIGNS – CROSS OVER
DESIGNS
Identified
sample of
subjects
Treatment 1A
Treatment 2B
Random
allocation
B Treatment 2
A Treatment 1

23. RCT’S DESIGNS- FACTORIAL
DESIGNS
Identified
sample of
subjects
Treatment 1A
Treatment 2B Random
allocation
C
D
Treatment 1+2
Control

24. RANDOMIZED CONTROLLED TRIALS
Disadvantages
 Patients are allocated to an undesired treatment
option where patient compliance may be low.
 Can be expensive and time consuming
 Often have too few patients or too short a follow-
up period
 Often imperfect randomisation