EPIDEMIOLOGICAL STUDIES II (Case Control, Experimental) Flashcards
(48 cards)
‘Trohoc’ Study: Opposite of cohort
Retrospective: go back to the past to check the exposure and why you have the outcome now at the present
Classify the outcome and will serve as the case
Analytic Observational
Direction of inquiry: past
Longitudinal: measuring variables at two different time point
Case-Control Studies
Outcome: start of the study
Exposure: some time in the past
Best design for diseases that are rare; rare outcomes and multiple exposure
Rare exposure, multiple outcomes: Cohort Study
Rare exposure and outcome: Case Series
Objective: to show that the probability of E is greater than in those with D+ than D-
Study groups are defined on the basis of presence or absence of the disease.
Outcome or disease is measured first
Study begins by selecting subjects based on the diseases, cases or outcome
Go back to the past to check for the exposure variables (exposed and non-exposed)
Case-Control Studies
The exposure status of the participants are then determined and compared between the study groups.
ODD MAN OUT: Advantages of Case-Control Studies 1. Quick and inexpensive 2. Suited to disease with long latency 3. Optimal for rare disease 4. Can examine multiple etiologic factors for a single disease 5. Vulnerable to bias
- Vulnerable to bias
ODD MAN OUT: Disadvantages of Case-Control Studies 1. Very cost-efficient 2. Inefficient for rare exposure 3. Cannot generate incidence of disease 4. Difficult to establish temporal sequence 5. Prone to bias
- Very cost-efficient
Steps in Case-Control Study: Diagnostic criteria for the disease Eligibility criteria Hospitals Population
Step 1: Define and select cases
Establish objective criteria
Select cases
Step 1: Define and select cases (Establish objective criteria)
tests are performed; PE, questionnaire
What outcome you would like to measure first
Diagnostic criteria for the disease
Step 1: Define and select cases (Establish objective criteria)
May be problematic if diagnostic procedure is expensive
Consider the price of the tests
Eligibility criteria
Step 1: Define and select cases (Select cases-sources)
secondary or case-defined base; available list of the disease
Hospitals
Step 1: Define and select cases (Select cases-sources)
primary study base
Population
Types of Cases:
____ : old + new cases
____: new cases; better type for case-control
Prevalent cases Incidence cases (Uniform diagnosis Accurate recall of exposure Temporal sequence)
Methods of selection of cases:
Total enumeration
Random sampling: larger population
Steps in Case-Control Study:
Most important and difficult aspect of the case-control design
Should represent the source population the cases arose from
Should not be influenced by the knowledge of the exposure status
Step 2: Definition and selection of controls
Step 2 (Definition and selection of controls): Comparable to the source of population cases Similar to the cases except for the disease of interest Difference should be the absence of the disease of interest Control should not have the disease of interest
Define control group
Matching -to achieve comparability
1-1 matching: 1 case: 1 control
Category matching: females: females
Step 2 (Definition and selection of controls): Get controls from the same source population as the case
Select control
Sources of Case and Control:
select controls from patients that are admitted for other reasons in the same hospital as the cases
Better recall of exposure, less time and money, cooperative
Patients may have come from different source population than the cases or other diseases may be associated with the exposure
Hospital
Sources of Case and Control:
neighborhood controls; select control from the same neighborhood as the cases
Source population is very clear
More time and money needed
Healthy control; no better recall of exposure
General population
Sources of Case and Control:
selecting the family or friends of the cases as the control group
Source population is very clear
Healthy but are motivated to participate in the study
Twin studies: best when want to remove potential effects of genetics
Special Groups
Methods of Case Control Sampling:
Random sampling Paired sampling (matched)
Steps in Case-Control Study:
Operational definition of exposure variable
Sources: subjects or medical records
Methods of data collection: same for the 2 groups (cases and controls)
Reference point should be identified: basis on which as individual should be considered exposed: to know who will be considered to be exposed and non-exposed
Step 3: Ascertainment of exposure
Steps in Case-Control Study:
No measure of disease frequency because research decides how many cases to recruit
Measures of association: Odds ratio (OR): estimate of risk
Step 4: Analysis
likelihood of the event occurring vs it is not occurring; used in Case-control # with characteristics / # without characteristics Minus # of with characteristics to the total population
Odds
risk (cohort); exposure risk # with characteristics / total unit
Probability
What Step?
“Living with a sputum positive adult Ptb case for one year is associated with development of Ptb in children 7 years old and below”
State the hypothesis in clear and specific terms
What Step?
Exposure: living with sputum positive adult Ptb case for 1 year
Outcome: development in Ptb in children 7 years old and below
Define study variables operationally
