Observational Studies Flashcards
1
Q
Types of descriptive study (3)
A
- Ecologic study
- Case report
- Cases series
2
Q
Types of analytical study (3)
A
- Cohort study
- Case-control study
- case-control nested within cohort study - Cross-sectional study
3
Q
Ecologic study measurement
A
- unit of observation is populations, not individual (exposure & outcome)
- prone to ecologic fallacy
4
Q
Ecologic fallacy definition
A
- when data collected at a population/group level are analysed & the results are assumed to apply to associations at the individual level
eg results from ecologic study are applied at individual level
5
Q
Strengths of Ecologic study (2)
A
- Inexpensive & easy to conduct
- usually using secondary data - Hypothesis generating
6
Q
Limitations of Ecologic study (2)
A
- Inability to link exposure to outcome in individuals
- ecologic fallacy - Likelihood of confounding by other variables
- due to observational studies only
7
Q
Case report & Case series studies
- definition
- uses
A
- careful & detailed reports of patient(s) with respect to factors that are potentially related to the illness/outcome
- case report (single patient)
- case series (series of patients)
- usually on unusual disease or association after first alert by an observant HCP
8
Q
Strength of Case report & Case series studies (1)
A
- Hypothesis generating
eg use in pharmacovigilance to pick up rare ADR
9
Q
Limitations of Case report & Case series studies (1)
A
No comparison group to assess association
10
Q
Assessment of causality in individual patients after case report / case series (3)
A
- Challenge (administer)
- Dechallenge (withdraw)
- Rechallenge (re-administer)
- if it is safe to rechallange
11
Q
Cross-sectional study
- definition
A
- information on presence/absence of exposure & outcome of individuals are assessed simultaneously at one point of time
- provides information about prevalence
12
Q
Strengths of Cross-sectional study (3)
A
- Efficient in terms of time & money
- Many outcomes & factors can be assessed
- No loss to follow up
13
Q
Limitations of Cross-sectional study (1)
A
Unclear temporal relation between exposure & outcome
- difficult to establish causal relationship as there is uncertainty whether exposure first then outcome or outcome first then exposure
14
Q
Cohort study definition (4)
A
- exposure to outcome
- classify on the basis of exposure
- compare on the basis of outcome
- baseline characteristics should be similar for both groups
15
Q
Examples of exposures of interests (4)
A
16
Q
Examples of outcomes of interests (2)
A
17
Q
Selection of unexposed group for Cohort study considerations
A
18
Q
Possible source of unexposed group for Cohort study (4)
A
- internal comparison (within same cohort)
- comparison cohort (another cohort)
- general population data (pre-existing data from general population)
- multiple comparison groups
19
Q
Strengths of Cohort study (4)
A
- Clear temporal sequence between exposure & outcome
- better able to suggest causality - Can study several outcomes associated with the drug
- Good for rare exposures
- Directly measure incidence of outcome
20
Q
Limitations of Cohort study (4)
A
- Not suitable for studying rare outcomes
- large sample size required - Inefficient
- study duration is long - Bias from the loss of follow up
- Costly
21
Q
Types of cohort study (2)
A
- Prospective cohort study
- outcome not occurred - Retrospective cohort study
- outcome alr occurred
22
Q
Prospective Cohort study
- strength (1)
- limitations (2)
A
Strength
- more control of the quality & quantity of data (less potential for bias)
Limitations
- more time consuming
- more expensive
23
Q
Retrospective Cohort study
- strengths (2)
- limitation (1)
A
Strengths (2)
- less time consuming
- less expensive
Limitation
- less control of the quality & quantity of data (greater potential for bias)
24
Q
Case-control study definition (3)
A
- outcome to exposure
- classify on the basis of outcome
- comparison on the basis of exposure
- careful selection of control group
25
Selection of cases for Case-control study
26
Selection of controls for Case-control study (4)
- represent population at risk of becoming cases
| - must be sampled independently of exposure
27
Examples of sources of cases for Case-control study (2)
- medical facilities
| - disease registries
28
Examples of sources of controls for Case-control study (2)
- hospitalised patients
| - general populations
29
Advantages of using hospitalised patients as source for control (4)
(Case-control study)
1. Convenient
2. Relatively inexpensive to identify & interview
3. Similar in their accuracy of recall
4. High level of cooperation of subjects
30
Disadvantages of using hospitalised patients as source for control (2)
(Case-control study)
1. Hospitalised patients may be hospitalised for diseases associated with risk factors under study
2. Selection factors leading to hospitalisation may differ (different referral patterns)
eg those no cancer cannot just take from 1 hospital, need to consider other hospitals
31
Advantages of using general population as source for control (1)
(Case-control study)
Ensures comparability
32
Disadvantages of using general population as source for control (4)
(Case-control study)
1. Difficult to conduct good random sampling
- dont have full list
2. Difficult to gain cooperation for participation
3. Relatively expensive to identify & interview
4. May not recall exposures with same degree of accuracy as cases
33
Strengths of Case-control study (5)
1. Ideal for study rare outcomes
2. Efficient to study outcomes that take a long time to develop
3. Can study multiple exposures/risk factors for a single outcome
4. More cost-efficient
5. Less time-consuming
34
Limitations of Case-control study (5)
1. Inefficient for studying rare exposures
- large sample size req
2. Difficulty in selection on control group (no outcome)
3. Difficulty in obtaining exposure data
4. Cannot estimate outcome rates directly but odd ratio
5. Potential bias when assessing exposure
- cos outcome alr known
35
Nested Case-control study definition (2)
- a case-control study "nested" within a cohort study
| - req cohort with banked specimens, images or information
36
Strengths of Nested Case-control study (3)
1. Efficiency in time & money
- 2 types of studies within a given period of time
2. Preserves all advantages of cohort studies
3. Avoids potential biases of conventional Case-control studies
37
Limitations of Nested Case-control study (2)
1. Most cohort studies does not have banked specimen, images or information
2. Nothing is gained by studying only a sample of controls when data for the entire cohort available at no additional cost
38
Reporting of Observational Studies
STROBE
STrengthing the Report of OBsevational studies Epidemiology
39
Types of observational studies (3+3)
- descriptive
- analytical
Descriptive
1. Ecologic study
2. Case report
3. Case series
Analytical
1. Cross-sectional study
2. Cohort study
3. Case-control study
40
Difference between the various observational studies (6)
1. Ecologic study
- descriptive
- at population level
2. Case report
- descriptive
- at individual level but single patient
3. Case series
- descriptive
- at individual level but consider several patients
4. Cross-sectional study
- analytical
- collect both exposure & outcome data at the same time
- unclear temporal relationship between exposure & outcome
5. Cohort study
- analytical
- differentiate patients based on exposure
- comparison based on outcome
6. Case-control study
- analytical
- differentiate patients based on outcome
- comparison based on exposure
41
Observational studies to use when :
- pick up rare outcomes
- assess association between drug & rare outcomes
Pick up rare outcomes
- case report / case series
Assess association between drug & rare outcomes
- case-control study
42
Criteria to do nested case-control study (2)
1. Cohort study first
| 2. Banked specimens, images or information
