Screening Flashcards
(28 cards)
What is lead time bias?
Screened individuals may appear to live longer because disease was detected earlier in its progression.
Lead time bias can skew the perception of survival rates in screened populations.
What is length time bias?
Cases identified by screening tend to be those with less aggressive disease because they have a longer DPCP.
DPCP stands for Disease Prevalence Cycle Period, influencing the types of cases detected.
What is volunteer bias?
Those who participate in screening programs may have different health behaviors or characteristics compared to those who do not.
This bias can affect the generalizability of screening study results.
What is sensitivity in the context of disease testing?
The proportion that tested positive for disease among those with disease.
The test has a ______% probability of correctly identifying as ‘positive’ those who actually have the disease.
[sensitivity percentage]
What is specificity in the context of disease testing?
The proportion that tested negative among those without disease.
The test has a ______% probability of correctly identifying as ‘negative’ those who do not in fact have the disease.
[specificity percentage]
What does Predictive Value Positive (PVP) indicate?
The proportion that have disease among those that test positive.
Among those who tested positive for disease using the test, _____% actually have the disease.
[PVP percentage]
What happens to Predictive Value Positive (PVP) if the prevalence of disease increases?
PVP will also increase.
What does Predictive Value Negative (PVN) indicate?
The proportion that do not have disease among those that test negative.
Among those who tested negative for disease using the test, _____% in fact do not have the disease.
[PVN percentage]
What happens to Predictive Value Negative (PVN) if the prevalence of disease decreases?
PVN will also increase.
How do you calculate sensitivity based on this chart?
Sensitivity = a/a+c
How do you calcuate specificity based on this chart?
Specificity = d/b+d
How do you calculate positive predicitive value based on this chart?
PPV = a/a+b
How do you calculate Negative Predictive Value based on this chart?
NPV = d/c+d
When is screening appropriate?
1) Serious disease with important health consequences
2) Early treatment is more effective than late
3) Disease has detectable preclinical phase (DPCP)
4) Prevalent DPCP with reasonably long duration in screened population
Screening should prioritize diseases that significantly impact health with benefits of early treatment.
What increases the effectiveness of screening?
Early treatment is more effective than later treatment
Timely intervention can lead to better health outcomes.
What is a detectable preclinical phase (DPCP)?
The interval of time that begins when the disease is detectable and ends at the manifestation of disease symptoms
DPCP helps identify when screening can be beneficial.
What is the significance of DPCP in screening?
It allows for the identification of disease before symptoms manifest
Screening aims to detect diseases during this phase for better outcomes.
What conditions should be met regarding the prevalence of DPCP?
The DPCP should be reasonably prevalent with a reasonably long duration in the population being screened
This ensures that screening programs are effective and beneficial.
What are the characteristics of a suitable screening test?
- Economical
- Convenient
- Relatively free of risk and discomfort
- Generally acceptable in the setting
- High validity
- High reliability
High validity means the test correctly identifies those with and without disease. High reliability means it gives the same result on repeated testing.
What does high validity in a screening test refer to?
Correctly identifies those with and without disease
Validity is crucial for ensuring that the screening test can accurately determine the presence or absence of a condition.
