screening sherine shawky, md, dr.ph assistant professor public health king abdulaziz university...
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Screening
Sherine Shawky, MD, Dr.PH
Assistant Professor Public Health
King Abdulaziz University College of Medicine
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Epidemiology in Medicine
Foundation of medical researchSupport for medical advancementEssential in medical education &
practiceBoundary for biostatistics
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Learning ObjectivesUnderstand the concept of
screeningUnderstand the characteristics of
health-related events suitable for screening
Recognize the characteristics of a screening program
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Performance Objectives
Apply screening for early detection of risk factors & diseases
Identify the factors suitable for screening
Evaluate the benefit of screening
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Screening
Screening is the process to detect among healthy
people disorders or risk factors of which they are
unaware
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Flow diagram for a screening program
Population
Test -ve Test +ve
Unaffected Affected
Intervention
Diagnostic procedures
Screening test
Re-screen Re-screen
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Types of screening
Mass Multiple or multiphasic Targeted Case-finding or opportunistic
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Factors appropriate for screening
Important health problemHigh prevalence Natural history understoodLong latent periodEarly detection improves prognosis
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Evaluation ofa screening program
ReliabilityFeasibilityValidityPerformanceEffectiveness
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Reliability
Biological variationProgram method Intraobserver variabilityInterobserver variability
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Feasibility
AcceptabilityQuickEasySafe
Cost effectivenessScreeningDiagnosisFollow-up Intervention
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ValiditySensitivity:
Probability to test positive among truly affected
Specificity: Probability to test negative among
truly unaffected
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PerformancePV+:- Probability to be affected
among test positivesPV-:- Probability to be unaffected
among test negativesPCC:- Probability to be correctly
classified
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Effectiveness
Outcome measures:MorbidityDisabilityMortality
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EffectivenessBias
Patient self-selection Lead timeLength
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Study designs for screening 1. Correlation Studies
Use:
Description of populationStrength:
Suggest possibility of benefitLimitation:
Can’t test hypothesis
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Study designs for screening 2. Analytical Studies
Types: Case-controlCohorts
Use: Comparison
of rates
Advantage: Test hypothesis
Limitation: Selection Lead time length
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Study designs for screening 3. Randomized Trials
Use:
Comparison of ratesStrength:
Most valid test of hypothesisLimitation:
Cost, ethics & feasibility
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Evaluation of screeningAffected+ - Total
+ TP FP SP
Scr
een
ing
- FN TN SNTotal TA TH GT
*Sensitivity= TP/TA *PV+ = TP/SP*Specificity= TN/TH *PV-= TN/SN *PCC= TP+TN/GT
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ConclusionObjectives of screening
Reduce disease incidenceReduce morbidity, disability &
mortalityCriteria for screening
Appropriate factorBeneficial program
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Review Questions (Developed by the Supercourse team)
• What is screening and what types of screening can you name?
• What are the objectives of screening?
• For what type of diseases would it be appropriate to set up screening programs? List characteristics.
• How is screening program evaluated?