S8: Screening Flashcards
What is the purpose of screening?
To give a better outcome compared with finding something the usual way - having symptoms and self-reporting to health services
If treatment can wait until there are symptoms there is no point in screening
Finding something earlier isn’t the primary objective
What are the five criteria of screening?
Can tiddies in Spain implode?
Condition - an important health problem
Test - simple, safe, precise and validated screening test
Intervention - effective intervention of patients identified through screening
Screening programme - proven effectiveness in reducing morbidity or mortality
Implementation - adequate staffing and facilities
Why is it important to evaluate screening programmes?
Screening programmes must be based on good quality evidence
What is lead-time bias?
Early diagnosis falsely appears to prolong survival
Screened patients appear to survive longer, but only because they were diagnosed earlier
What is length-time bias?
Screening programmes are better at picking up slow-growing unthreatening cases than aggressive, fast-growing ones
Diseases picked up through screening are more likely to have a favourable prognosis and may have never caused a problem
What is selection bias?
Studies of screening are often skewed by having a “healthy volunteer” effect.
Those who opt for screening are more likely to engage in better health behaviour and so have better health outcomes overall
What are the two types of error a screening test can make?
False-positive - referring well people for further investigation
False-negative - fail to refer people who actually have an early form of the disease
What are the features of test validity?
Sensitivity
Specificity - these two refer to people with/ without the disease
Positive predictive value
Negative predictive value - these two refer to people who have taken the test
