ASDA: Population Based Screening Flashcards
Define screening.
A systematic attempt to detect an unrecognised condition using test which can be applied rapidly to distinguish between apparently well persons who probably have a disease and those who do probably not.
Name the criteria for implementing a screening program.
- Condition
- Test
- Intervention
- Screening program
- Implementation
Describe how the following is important when determining the criteria for implementing a screening program:
Condition
It has to be an important health problem (frequency/severity) whose natural history is understood.
All cost effective primary prevention interventions should have been implemented before screening.
Describe how the following is important when determining the criteria for implementing a screening program:
Test
Must have a known distribution of test values and be safe, simp,e, precise and validated.
Describe how the following is important when determining the criteria for implementing a screening program:
The intervention or treatment.
There needs to be evidence that intervention at a pre-symptomatic phase leads to better outcomes.
Describe how the following is important when determining the criteria for implementing a screening program:
The program itself.
Must have proven effectiveness in reducing mortality or morbidity.
There must also be evidence the the screening program is clinically, socially and ethically acceptable to HCW and the public.
Describe how the following is important when determining the criteria for implementing a screening program:
The implementation
There must be quality assurance and adequate staffing.
Public pressure should be anticipated.
Name the difficulties of evaluating the effectiveness of screening programs.
- Lead time bias
- length time bias
- selection bias
Describe why the following makes evaluation of screen programs difficult:
Lead time bias.
Early diagnosis falsely appears to prolong survival only because they were picked up earlier than they would have been.
Describe why the following makes evaluation of screen programs difficult:
Length time bias.
Screening programs are better at picking up slow growing unthreatening cases than aggressive, fast-growing ones.
Describe why the following makes evaluation of screen programs difficult:
Selection bias.
Healthy worker effect, i.e. Those that are lie,lay to have regular screening are also more likely to take other precautions that protect from the disease.
What is the sensitivity (deception rate)?
The proportion of pope with the disease who are test positive.
How do you calculate the sensitivity rate?
True positives/ true positives+false negatives
What does the result of a sensitivity test calculation mean?
If the sensitivity is high the test is very good.
What is specificity?
The proportion of people without the disease who test negative.
