EPIDEMIOLOGICAL STUDIES II (Case Control, Experimental) Flashcards
‘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
What Step?
≤ 7 year old children residing in barangay X
Define study population
What Step?
Case: ≤ 7 year old children who has Ptb based on WHO criteria of the disease
Control: same source of population; neighborhood not living with sputum positive adult Ptb case for a year or other sources like special group
Define and select a case and control
What Step?
method should be same as case and control
History of exposure to the factor
Reference point: exposure should have occurred at least 12 months before the diagnosis of Ptb
Method: Face-to-face interview
Data collection
“there is an association and exposure is a risk factor”
Analysis
Odds ratio
1: no association
>1: association, risk factor
<1: association, protective factor
Interpretation
Analytical, prospective, and experimental type of study
Study comparing the effects and value of intervention against the control in human being
Investigator manipulates the exposure assigned to the participants in the study
Investigators intervenes in one group and withholds intervention in another group
Experimental Studies
have the exposure at the start of the study and outcome sometime in the future
Prospective
there is manipulation and assignment of exposure variable
Similar with cohort but is observational; no assigning and manipulation; prospective observational study
Compare effects and value
Experimental
Characteristics of Experimental Studies:
Independent and dependent variables
Exposure and outcome
Treatment and effect
Involves a test hypothesis
Characteristics of Experimental Studies:
Individuals are enrolled on the basis of their exposure status
Entire group is followed up and monitored
Prospective
Characteristics of Experimental Studies:
Investigators allot exposure by applying randomized allocation scheme
Purpose: create groups that differ only randomly at the time of allocation with regard to subsequent occurrence of the study outcome
Random allocation of study subjects
Characteristics of Experimental Studies:
Intervention group: receives the treatment
Control group: withhold from the treatment
Comparison group
Classification of Experimental Studies according to Type of subjects/ unit of analysis:
Patients as subjects
Randomized clinical trials (RCT)
Classification of Experimental Studies according to Type of subjects/ unit of analysis:
Interventions assigned to individual community members
Subjects are not defined by presence or absence of the disease but by the initial occurrence of the disease (Community settings)
Field trials
Classification of Experimental Studies according to Type of subjects/ unit of analysis:
Interventions assigned to whole communities
Group level intervention
Community intervention trials
Classification of Experimental Studies according to Purpose:
Agent is administered to determine its effects on controlling or treating the diseases
Conducted among patients with a particular disease to determine the ability of an agent to procedure or diminish symptoms, prevented occurrence or decrease risk of death from the disease
Study population: persons with disease
Therapeutic (secondary prevention)
Classification of Experimental Studies according to Purpose:
Agent is administered or procedure is performed to determine its effect on preventing the disease
Evaluation of whether an agent or procedure reduces the risk of developing the disease among those free from the disease at enrollment
Study population: person without disease
Preventive (primary prevention)
Classification of Experimental Studies according to Treatment modality:
Most widely used design in clinical research
Compare outcomes observed in two or more groups of subjects or patients who received different interventions
Effects on the dependent variable for one subjects or group of subjects are compared with the effect for another subject or another group of subjects
Between subjects design (parallel group design)
Classification of Experimental Studies according to Treatment modality:
All subjects experience all treatments in succession but order vary; groups experiences all the treatment only difference is the order of treatment
Repeated measurement of the outcomes in each subject
Needs less participants for they will be counted twice
Wash out period: allows the body to remove the first intervention taken, to minimize residual effect
Within subjects design (cross-over design)
Effects on the dependent variable for an experimental condition and for the controlled condition are compared within one person
Applicable for outcomes that are reversible
Time consuming and expensive but gives credible data (both will receive both treatment)
Classification of Experimental Studies according to Treatment modality:
Used to test two or more hypothesis simultaneously
Subjects are first randomized to treatments A & B to address one hypothesis
Within each treatment group there is further randomization to treatments evaluate a second question
Same group of subjects (factorial design)
Classification of Experimental Studies according to Phase of development of a treatment (RCTs):
determine the pharmacologic and metabolic effects of the drug in human study. Subjects are human volunteers
First used in experimental animals before human
Phase I
Classification of Experimental Studies according to Phase of development of a treatment (RCTs):
new treatment is tried for the first time in the type of patients for whom the treatment is intended
Dosing studies for optimal dose
Phase II
Classification of Experimental Studies according to Phase of development of a treatment (RCTs):
treatment is brought to real-life situation with outcomes considered to be
Clinically relevant in patients diagnosed with the indication for the treatment
Phase III
Classification of Experimental Studies according to Phase of development of a treatment (RCTs):
post marketing (surveillance) trial
Side effects cause over time by the treatment is still being studied
Look for the other side effects that were not seen in other trials
Also study how well a treatment works over a long period of time
Phase IV
