Screening Sherine Shawky, MD, Dr.PH Assistant Professor Public Health King Abdulaziz University College of Medicine

Epidemiology in Medicine  Foundation of medical research  Support for medical advancement  Essential in medical education & practice  Boundary for biostatistics

Learning Objectives  Understand the concept of screening  Understand 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 -veTest +ve UnaffectedAffected Intervention Diagnostic procedures Screening test Re-screen

Types of screening  Mass  Multiple or multiphasic  Targeted  Case-finding or opportunistic

Factors appropriate for screening  Important health problem  High prevalence  Natural history understood  Long latent period  Early detection improves prognosis

Evaluation of a screening program  Reliability  Feasibility  Validity  Performance  Effectiveness

Reliability  Biological variation  Program method  Intraobserver variability  Interobserver variability

Feasibility  Acceptability  Quick  Easy  Safe  Cost effectiveness  Screening  Diagnosis  Follow-up  Intervention

Validity  Sensitivity: Probability to test positive among truly affected  Specificity: Probability to test negative among truly unaffected

Performance  PV+:- Probability to be affected among test positives  PV-:- Probability to be unaffected among test negatives  PCC:- Probability to be correctly classified

Effectiveness  Outcome measures :  Morbidity  Disability  Mortality

Effectiveness  Bias  Patient self-selection  Lead time  Length

Study designs for screening 1. Correlation Studies  Use: Description of population  Strength: Suggest possibility of benefit  Limitation: Can’t test hypothesis

Study designs for screening 2. Analytical Studies  Types:  Case-control  Cohorts  Use:  Comparison of rates  Advantage:  Test hypothesis  Limitation:  Selection  Lead time  length

Study designs for screening 3. Randomized Trials  Use: Comparison of rates  Strength: Most valid test of hypothesis  Limitation: Cost, ethics & feasibility

Evaluation of screening *Sensitivity= TP/TA *PV+ = TP/SP *Specificity= TN/TH *PV-= TN/SN *PCC= TP+TN/GT

Conclusion  Objectives of screening  Reduce disease incidence  Reduce morbidity, disability & mortality  Criteria for screening  Appropriate factor  Beneficial 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?