Screening (Statistics) Flashcards
Define screening
Systematic population based approach to identifying healthy people at higher risk of a health problem, so that early treatment or intervention can be offered, or information given to help them make informed decisions
e.g. Newborn hearing screening, diabetic eye screening, breast screening
Results are no diagnostic e.g screening = mammography diagnosis = triple assessment
What does a positive screening result mean?
High risk
Further investigations
For example, testing positive for HPV in cervical screening will result in cytology (smear test), followed by colposcopy if needed.
Advantages of screening?
Typically quick and cheap
May relieve anxieties
Reduce risk of exacerbation and death
Disadvantages of screening?
False positives may lead to anxiety, and harm caused by unnecessary tests
Screening results are frequently misunderstood and cause anxiety and stress
Can be invasive
False negative may falsely reassure and cause symptoms to be ignored
Sensitivity
Proportion of individuals WITH the disease that test positive
True positives/True positives and false negatives
A highly sensitive test can rule out a disease
Specificity
Propertion of individuals WITHOUT the disease that test negative
True negatives/True negatives and false positives
A highly specific test can rule in disease
Positive predictive value PPV
True positive rate
The proportion of individuals who test positive for the disease who actually have the disease
True positives/true positives and false positives
Negative predictive value NPV
True negative rate
The proportion of individuals who test negative for a disease who do not have the disease
True negatives/true negatives and false negatives
Difference between Sensitivity/Specificity and PPV/NPV
S/S = inherent to the screening test
PPV/NPV = dependant on disease prevalence
