1. EPIDEMIOLOGICAL STUDIES
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2. OUTLINE
 Classification of studies
 Study Designs and analysis
 Choice of study design
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3. CLASSIFICATION
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4. CLASSIFICATION
 Various ways
 BUT, two major classes
 Non-Interventional
 Interventional
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5. Non-Intervention studies
 Researcher do not manipulate
situations/objects
 Just describes or analyses
situations/objects
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6. Intervention studies
 Researcher manipulates
situations/objects then describes or
analyses the outcome
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7. STUDY DESIGNS AND ANALYSIS
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8. Non-Intervention studies
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9. Types of Non- Interventional studies
 Exploratory
 Descriptive
 Analytical
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10. Exploratory studies
 Small scale studies
 Gathers information about unfamiliar
phenomenon
 Results gives insight to a problem
before a large scale study is designed
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11. Descriptive studies
 Only describe phenomena: e.g. Person,
Place, Time
 No analysis of determinants/association
 E.g. Cross-sectional descriptive
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12. Cross-sectional descriptive
 Aim at just describing phenomenon
 Done at one point in time – hence
Cross-sectional
 E.g. Prevalence studies, KAPB studies
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13. Analytical studies
 Describe phenomena
 And
 Analyze relationship between
phenomena and other variables
(determinants/association).
 Examples:
 Cross-sectional comparative
 Cohort study
 Case-control study
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14. Cross-sectional comparative study
 Aim at describing phenomenon and
compare groups or determine factors
influencing the phenomenon
 Done at one point in time
 Measurement of exposure and
effect are done at the same time
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15. Advantages and Disadvantages
of Cross-sectional studies
Advantages Disadvantages
 Quick and cheap  Not possible to determine
 Can elucidate various if the exposure preceded
exposures, as first the outcome (temporal
step in investigating relationship)
cause
 Bias**
 Repeated measures
can depict trend
 Data useful in
assessing health care
needs
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16. Cohort studies
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17. Cohort study (“Prospective, “Follow
up” study)
 Aim at determining risk factors for
diseases/outcome
 At the start identify two groups
 With exposure to a risk factor (exposed)
 Without exposure (no-n exposed)
 Both groups have not developed the
disease/outcome at the start
 Follow over time
 At the end, analyse disease/outcome
occurrence in both groups and compare
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18. Design of Cohort study - I
 Time
 Inquiry
Disease
Start
Exposed No disease
Population Non-diseased
people
Non-exposed
Disease
No disease
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19. Design of Cohort study - II
 Exposed and non-exposed groups
must be comparable in all factors that
may be related to the disease except
for the exposure
 Need to get complete and accurate
information about exposure and
outcome for all individuals
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20. Analysis of Cohort studies
 Compare incidences of disease among
exposed to non-exposed group
 Cumulative incidence (Calculate Relative
Risk) (commonly)
 Incidence rate (Calculate Incidence rate
ratio), - when person time of follow up is
known
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21. Advantages & Disadvantages
 Advantages  Disadvantages
 Allows direct  Time consuming,
measurement of expensive
incidence of disease  Inefficient in
 Multiple effects of evaluating rare
single exposure can be diseases
examined  Loss of follow up affect
 Can elucidate temporal validity of results
relationship between
exposure and disease
 Is of value when
exposure is rare
 Minimize bias in
ascertainment of
exposure
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22. Case – control studies
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23. Case –control study
(“Retrospective” study)
 Aim at determining risk factors for
diseases/outcome
 At the start identify two groups
 With disease/outcome (Cases)
 Without disease/outcome (Controls)
 History of exposure to risk factor is
inquired
 At the end, analyse exposures to a risk
factor in both groups and compare
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24. Design of Case-control study - I
 Time Start
 Inquiry
Exposed
Cases
Non exposed Population
Exposed
Controls
Non expose
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25. Design of Case-control study - II
 Controls should be representative of the population from
which the cases are recruited
 Cases and controls must be comparable in all factors
that may be related to the disease except for presence
of disease
 Controls can be chosen to match cases for certain
important variables such as age, sex, etc = Matched
Case-control design. If matching not done = Un-
matched case-control design (more common)
 Need to get complete and accurate information about
exposure for all individuals
 Control: Case ratio? Consider cost, availability of cases
 Usually ratio of 1:1 up to 4:1, beyond that no added
advantage for power of the study
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26. Analysis of Case-control studies
 Compare Exposure of disease among
Cases to Controls
 Calculate Odds Ratio
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27. Advantages & Disadvantages
 Advantages  Disadvantages
 Relatively quick  Inefficient in
and inexpensive evaluating rare
 Suitable for rare exposures
diseases  Temporal
 Can evaluate relationship
effect of multiple between exposure
exposures and disease difficult
 Is of value for to ascertain
diseases with long  Prone to recall bias
latent periods
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28. Intervention studies
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29. Intervention studies
Two main types:
 Experimental (Classical experiment)
 Quasi-experimental
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30. Characteristics of Experimental studies
 Manipulation
 Something is done to one group
(experimental group)
 Presence of Control group (no manipulation
done)
 Randomization (assignment of individuals to
experimental or control groups is done
randomly)
 Example: Randomized Controlled Trials
(RCT) – “Gold standard”
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31. Characteristics of Quasi-Experimental
studies
 Manipulation
 Control group or Randomization missing
 Example: Community trials
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32. Design of Randomized controlled trial - I
Exp. group
Follow up &
Study Analysis
General pop Randomization
PX
Control group
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33. Design of Randomized controlled trial - II
 Randomization ensures that chance alone determines
which individuals become experimental group and
which ones become control group
 Thus, making the groups comparable in most aspects
that may be related to the outcome
 Design provide strong evidence of the effect of the
intervention – “Gold standard”
 Study participants are blinded about the intervention
(Single blind)
 Sometimes both Study participants and investigators
are blind about the intervention (Double-blind)
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34. Ethical Considerations in Experimental studies
 Carried out only if:
 Evidence suggest intervention is
beneficial, but uncertain of effect
 No serious adverse effect to the
intervention group
 Informed consent to participate
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35. Analysis of Intervention studies
 Comparison of outcome of interest in
experimental and control groups
 Comparison of baseline
characteristics of experimental and
control groups
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36. Choosing a study design
Considerations:
 Ethical issues – minimal ethical
concerns
 Resources and administrative issues
 Validity and reliability of results
 Nature of topic
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