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
Epidemiology in Medicine
Foundation of medical researchSupport for medical advancementEssential in medical education &
practiceBoundary for biostatistics
Learning ObjectivesUnderstand the concept of
screeningUnderstand the characteristics of
health-related events suitable for screening
Recognize the characteristics of a screening program
Performance Objectives
Apply screening for early detection of risk factors & diseases
Identify the factors suitable for screening
Evaluate the benefit of screening
Screening
Screening is the process to detect among healthy
people disorders or risk factors of which they are
unaware
Flow diagram for a screening program
Population
Test -ve Test +ve
Unaffected Affected
Intervention
Diagnostic procedures
Screening test
Re-screen Re-screen
Types of screening
Mass Multiple or multiphasic Targeted Case-finding or opportunistic
Factors appropriate for screening
Important health problemHigh prevalence Natural history understoodLong latent periodEarly detection improves prognosis
Evaluation ofa screening program
ReliabilityFeasibilityValidityPerformanceEffectiveness
Reliability
Biological variationProgram method Intraobserver variabilityInterobserver variability
Feasibility
AcceptabilityQuickEasySafe
Cost effectivenessScreeningDiagnosisFollow-up Intervention
ValiditySensitivity:
Probability to test positive among truly affected
Specificity: Probability to test negative among
truly unaffected
PerformancePV+:- Probability to be affected
among test positivesPV-:- Probability to be unaffected
among test negativesPCC:- Probability to be correctly
classified
Effectiveness
Outcome measures:MorbidityDisabilityMortality
EffectivenessBias
Patient self-selection Lead timeLength
Study designs for screening 1. Correlation Studies
Use:
Description of populationStrength:
Suggest possibility of benefitLimitation:
Can’t test hypothesis
Study designs for screening 2. Analytical Studies
Types: Case-controlCohorts
Use: Comparison
of rates
Advantage: Test hypothesis
Limitation: Selection Lead time length
Study designs for screening 3. Randomized Trials
Use:
Comparison of ratesStrength:
Most valid test of hypothesisLimitation:
Cost, ethics & feasibility
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
ConclusionObjectives of screening
Reduce disease incidenceReduce morbidity, disability &
mortalityCriteria for screening
Appropriate factorBeneficial program
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?