biomed lec3 day
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Study Populations
Simon Day, PhDJohns Hopkins University
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Identifying the Study Population
The study population should be defined in advance, stating
unambiguous inclusion (eligibility) criteria. The impact that these
criteria will have on study design, ability to generalize, and
participant recruitment must be considered.Friedman, et al., pg. 30
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Study Population
Eligibility = inclusion + exclusion criteria Consider . . .
Feasibility Generalizability
Risk/benefit Subject characteristics
Disease characteristics
Enrichment
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Population at large
Population with condition
Study population
Study sample
Overall Picture
Definition of
condition
Entry
criterion
Enrollment
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Population at large
Women with breast cancer
HER2+, distant metastases, no prior chemotherapy, no serious
intercurrent illness
Study sample
Definition of
condition
Entry
criterion
Enrollment
Example: Women with Breast Cancer
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Population at large
Population with condition
Study population
Study sample
How It Happens in Practice
Population
w/o condition
Withcondition
but ineligible
Eligible
but not
enrolled
Definition of
condition
Entry
criteria
Enrollment
And these we randomize
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Eligibility Criteria
Identify subjects: Likely to benefit In whom benefit can be discerned
In whom risks are acceptable
Function of trial phase and objectives
Basis for generalizability of results
Improve precision of effect
Quantitative or otherwise clearly interpretable criteria should beused
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Eligibility Criteria
InclusionHospitalized patients 18
years-of-age or older
Oral temperature >38.5 C
ExclusionHistory of hypersensitivity
to new treatment (and
control)
Pregnant or breastfeedingHospitalized for CHD or for
treatment of endocarditis
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An Example in Obesity
The epidemiology 20% adults BMI > 30increases with age At least 20% of all patients would fall into a high-risk category
50% of these high-risk patients will have a BMI > 27
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Epidemiology
Taking any 100 adults on GP list: 20 patients will have a BMI > 30 10 patients will have at least one risk factor and BMI > 27 Allowing for overlap and ineligibles, it was estimated that 20 adults
out of every 100 will qualify
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Mailshots and advertisingMailshot known
high-risk patients
32 Patients formally
consented and screened
40% selected for
screening
320 Responses fortelephone screening
80 Patients pre-screened
25% success rate
20 Patients randomised and
treated with study
medication
Enrolment successrate following formal
screening
Anticipated Recruitment Funnel
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A Critical Question . . .
To whom do the results apply? All patients? All patients who meet the disease criteria?
All patients who meet the disease criteria but are not subject
to any of the exclusion criteria?
All patients who . . . [as above] . . . and who are willing to takepart in a trial? Your next patient?
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In the Next Lecture Well Look at . . .
Study designs issues Randomization Blinding (masking)
Stratification, blocking