This document discusses different types of epidemiological study designs, including descriptive and experimental designs. Descriptive designs include cross-sectional studies, case reports, case series, and qualitative studies. Cross-sectional studies examine the relationship between diseases and other factors in a population at a single point in time. Case reports and case series describe characteristics of individual patients or small groups. Experimental designs include randomized controlled trials (RCTs) which test the effectiveness of interventions by randomly assigning participants to intervention or control groups. Observational studies like case-control and cohort studies examine the relationship between exposures and outcomes without intervention. The document outlines advantages and disadvantages of each design.

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06/15/13
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Dr. Nisreen A. Jastaniah
Assist Prof KSAU-HS
Consultant Geriatric Medicine KAMC-J
Types Of Epidemiological StudiesTypes Of Epidemiological Studies
(Study Design)(Study Design)

2. Study Design
Research :
Diligent inquiry or examination in seeking facts.
Laborious or continued search after the truth.
Systematic investigation towards increasing the sum of
knowledge.
An endeavour to discover new or collect old facts by
the scientific study of a subject or by a course of
critical investigation.

3. Study Design
Study design:
Is the master plan specifying the methods and procedures
for collecting and analyzing the needed information.
The choice of the most appropriate design depends
largely on the objectives

4. Study Design
Question –Related- (P patient , I intervention ,
C comparison group , O outcome , T time )
F feasible
I interesting
N novel
E ethical
R relevant

5. Study design
LongitudinalDescriptive
Cross sectional
Case report
Case series
Interventional
(RCT)Observational
Case-control
Cohort
Study DesignStudy Design

6. Study DesignStudy Design DescriptiveDescriptive
(Cross sectional)(Cross sectional)
Qualitative study
A qualitative study explores people’s subjective
understandings of their life and experiences.
Methods used include
– Direct observation
– Interviews
– The analysis of texts or documents or recorded
speech or behavior

7. Study DesignStudy Design DescriptiveDescriptive
(Cross sectional)(Cross sectional)
Qualitative studies
Advantages
• Obtain views, opinions and perspectives of
individuals included in the study
• Identify themes that could may not been identified
from a quantitative study
Disadvantages
• Generalizabiltiy

8. Study DesignStudy Design DescriptiveDescriptive
(Cross sectional)(Cross sectional)

9. Study DesignStudy Design DescriptiveDescriptive
(Cross sectional)(Cross sectional)

10. Study DesignStudy Design DescriptiveDescriptive
CASE EPORT/SERIESCASE EPORT/SERIES
CASE REPORT/SERIES
Describe patients’ characteristics, and may generate ideas for future studies

11. Study DesignStudy Design DescriptiveDescriptive
CASE REPORT/SERIESCASE REPORT/SERIES
Advantages
• Useful when the disease is uncommon
• First to provide clues to identify a new disease or
adverse effect
Disadvantages
• Usually small sample size
• Only of minor relevance to public health

12. Study DesignStudy Design DescriptiveDescriptive
CASE REPORT/SERIESCASE REPORT/SERIES

13. Study DesignStudy Design Longitudinal-observationalLongitudinal-observational
Case-control studyCase-control study
Disease
No disease
(control)
Yes
No
Yes
No
Starting point
History of exposure
Compare & draw conclusions

14. Study DesignStudy Design Longitudinal -ObservationalLongitudinal -Observational
Case-control studyCase-control study
Advantages of
case – control studies
 Quick
 Require reasonably small numbers
 Reasonably economical
 Sensible for study of rare diseases
 No loss to follow – up
 Can test current hypotheses

15. Study DesignStudy Design Longitudinal - observationalLongitudinal - observational
Case-control studyCase-control study
Disadvantages of case – control studies
 Uncertain if exposure preceded disease
 Potential for recall bias (sick people may be more [or less]
likely to recall exposure)
 Selection bias (recruitment influenced by exposure)

16. Longitudinal - observationalLongitudinal - observational
Case-control studyCase-control study

17. Longitudinal – ObservationalLongitudinal – Observational
Exposed
Not exposed
(control)
Yes
No Yes
No
DiseaseFollow up
Starting point
Compare & draw conclusions
Cohort studies

18. Longitudinal – ObservationalLongitudinal – Observational
Cohort StudiesCohort Studies
Advantages of Cohort Study
• Can collect exposure information as exposure
happens
• Can collect multiple different exposures
• Exposure information should be relatively
reliable
• Can collect information as outcome happens

19. Longitudinal – ObservationalLongitudinal – Observational Cohort StudiesCohort Studies
Disadvantages of cohort studies
• Duration of study: may take decades to complete
• Subjects must be followed over time
• Cost: very expensive
Can you afford to wait decades for your answer?

20. Longitudinal – ObservationalLongitudinal – Observational Cohort StudiesCohort Studies

21. Longitudinal – ObservationalLongitudinal – Observational Cohort StudiesCohort Studies

22. Longitudinal – ObservationalLongitudinal – Observational

23. Study Design & Evidence Based Clinical PracticeStudy Design & Evidence Based Clinical Practice
Different questions study design
Prevalence or frequency of factor Cross sectional
Hypotheses about possible Harm (or causes) Case-control
Harm or Causes or risk factors Cohort
Experience of illness Qualitative
Effectiveness RCT

25. Experimental Study Design
Study design
LongitudinalDescriptive
Cross sectional
Case report
Case series
interventionalobservational
Case-control
cohort

26. Experimental Study Design
A type of research that tests how well new medical
approaches work in people. These studies test new
methods of screening, prevention, diagnosis, or
treatment of a disease.

27. Experimental Study Design
controlled clinical trial
A clinical study that includes a comparison (control) group. The
comparison group receives a placebo, another treatment, or no
treatment at all.

28. Experimental Study Design
 Clinical trial
sample
intervention
control
Yes
No Yes
Noinclusion
exclusion
improved

29. Experimental study design
Exclusion criteria
Be parsimonious
Compelling (clinical
characteristics).
(?follow-up , compliance , high
risk).
Inclusion Criteria
Be specific
Specify populations relevant to
study question
(Demographic , Geographic ,
clinical characteristics).

30. Experimental Study Design
Random Assignment
Comparable groups
(Treatment & Control)
confounding variable
Is a variable in a one
group that correlate
(positively or
negatively) with the
outcome
Sample
I C
Random Allocation

31. Experimental Study Design
intervention group (I)
The group receiving the study agent that
is being tested in a clinical trial or
clinical study
Control group:
In a clinical trial, the group that does not
receive the new treatment being
studied.

32. Experimental Study Design
Blinding;
Eliminates unintentional prejudices by
those involved…
honest answers
(Single blind , double blind)
both the patients and the research staff do
not know and cannot figure out which
patients are receiving treatment and
which placebo.
Co-intervention & contamination
Blind
Co-intervention
I C

33. Experimental Study Design
S
I C
Drop-out
Dropout
The loss of participants during the
course of a study. (Also called loss to
follow up.)
more than 20 percent
Intention to treat

34. Experimental Study Design
Disadvantage
Most costly & time consuming
Randomization, blinding, placebos…
Not feasible for outcomes that are
rare or have long lag times
Sample may be very restrictive
making extrapolation difficult
Advantage
Potential for bias & confounding is
theoretically eliminated
Best design to establish cause & effect

36. Good Work …. Team Work
Choose mentor wisely
Get an epidemiologist / statistician

37. Study Design
Study design
LongitudinalDescriptive
Cross sectional
Case report
Case series
interventionalobservational
Case-control
cohort

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