Download Intervention studies

EPIDEMIOLOGICAL STUDIES
1
OUTLINE
 Classification of studies
 Study Designs and analysis
 Choice of study design
2
CLASSIFICATION
3
CLASSIFICATION
 Various ways
 BUT, two major classes
 Non-Interventional
 Interventional
4
Non-Intervention studies
 Researcher do not manipulate
situations/objects
 Just describes or analyses
situations/objects
5
Intervention studies
 Researcher manipulates
situations/objects then describes or
analyses the outcome
6
STUDY DESIGNS AND ANALYSIS
7
Non-Intervention studies
8
Types of Non- Interventional studies
 Exploratory
 Descriptive
 Analytical
9
Exploratory studies
 Small scale studies
 Gathers information about unfamiliar
phenomenon
 Results gives insight to a problem
before a large scale study is designed
10
Descriptive studies
 Only describe phenomena: e.g. Person,
Place, Time
 No analysis of determinants/association
 E.g. Cross-sectional descriptive
11
Cross-sectional descriptive
 Aim at just describing phenomenon
 Done at one point in time – hence
Cross-sectional
 E.g. Prevalence studies, KAPB studies
12
Analytical studies
 Describe phenomena
 And
 Analyze relationship between
phenomena and other variables
(determinants/association).
 Examples:
 Cross-sectional comparative
 Cohort study
 Case-control study
13
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
14
Advantages and Disadvantages
of Cross-sectional studies
Advantages
 Quick and cheap
 Can elucidate various
exposures, as first
step in investigating
cause
 Repeated measures
can depict trend
 Data useful in
assessing health care
needs
Disadvantages
 Not possible to determine
if the exposure preceded
the outcome (temporal
relationship)
 Bias**
15
Cohort studies
16
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
17
Design of Cohort study - I

Time

Inquiry
Disease
Start
Exposed
Population
No disease
Non-diseased
people
Non-exposed
Disease
No disease
18
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
19
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
20
Advantages & Disadvantages
 Advantages





Allows direct
measurement of
incidence of disease
Multiple effects of
single exposure can be
examined
Can elucidate temporal
relationship between
exposure and disease
Is of value when
exposure is rare
Minimize bias in
ascertainment of
exposure
 Disadvantages



Time consuming,
expensive
Inefficient in
evaluating rare
diseases
Loss of follow up affect
validity of results
21
Case – control studies
22
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
23
Design of Case-control study - I
 Time
 Inquiry
Exposed
Start
Cases
Population
Non exposed
Exposed
Controls
Non expose
24
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 = Unmatched 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
25
Analysis of Case-control studies
 Compare Exposure of disease among
Cases to Controls
 Calculate Odds Ratio
26
Advantages & Disadvantages
 Advantages
 Relatively quick
and inexpensive
 Suitable for rare
diseases
 Can evaluate
effect of multiple
exposures
 Is of value for
diseases with long
latent periods
 Disadvantages
 Inefficient in
evaluating rare
exposures
 Temporal
relationship
between exposure
and disease difficult
to ascertain
 Prone to recall bias
27
Intervention studies
28
Intervention studies
Two main types:
 Experimental (Classical experiment)
 Quasi-experimental
29
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”
30
Characteristics of Quasi-Experimental
studies
 Manipulation
 Control group or Randomization missing
 Example: Community trials
31
Design of Randomized controlled trial - I
Exp. group
General pop
Study
PX
Follow up &
Analysis
Randomization
Control group
32
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)
33
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
34
Analysis of Intervention studies
 Comparison of outcome of interest in
experimental and control groups
 Comparison of baseline
characteristics of experimental and
control groups
35
Choosing a study design
Considerations:
 Ethical issues – minimal ethical
concerns
 Resources and administrative issues
 Validity and reliability of results
 Nature of topic
36