Module 3 Lecture 26

Question 1

Screening in health

Answer 1

Screening involves identifying unrecognised disease or risk factors for disease by applying tests on a large scale population

Question 2

The less expensive diagnostic test is the _______ and the more expensive, more _______ diagnostic test is the _______

Answer 2

Screening Test; invasive; Gold Standard Test

Question 3

The screening criteria are

Answer 3

Suitable disease, suitable test, suitable treatment. suitable screening programme

Question 4

What is the objective of the screening initiative

Answer 4

To improve health outcome

Question 5

Suitable disease

Answer 5

1) An important public health problem:
- Relatively common
- Relatively uncommon ( early detection –> better outcome)
2) Knowledge of the natural history of the disease: detectable early, increased duration of pre clinical phase (early features of disease to clinical diagnosis)

Question 6

A suitable test must be….

Answer 6

Reliable, Safe, Acceptable, Simple, Cheap and Accurate

Question 7

Sensitivity

Answer 7

• The ability of the test to identify correctly those who have the disease from all individuals with the disease
• The likelihood of a positive test in those with the disease
• True Positives/All with disease x 100

Question 8

Specificity

Answer 8

• The ability of the test to identify correctly those who do not have the disease from all individuals free from the disease
• The likelihood of a negative test in those without the disease
• True Negatives/All without disease x 100

Question 9

Positive Predictive Value (PPV)

Answer 9

• The proportion who really have the disease of all people who test positive
• The probability of having disease if the test is positive
• True positives/all who test positive x 100

Question 10

Negative Predictive Value (NPV)

Answer 10

• The proportion who are actually free of the disease of all people who test negative
• The probability of not having the disease if the test is negative
• True negatives/all who test negative x 100

Question 11

Suitable Treatment

Answer 11

• Evidence of early treatment leading to better outcomes
• Effective, acceptable and accessible treatment
• Evidence-based policies covering who should be offered treatment and the appropriate treatment to be offered

Question 12

Suitable Screening Programme

Answer 12

• Benefits must outweigh harm

- RCT evidence that screening programme will result in reduced mortality and increased survival time

Question 13

Lead time bias

Answer 13

Survival after screening - Survival after diagnosis is the lead time and if not evaluated in these terms gives a false impression of success

Question 14

Length time bias

Answer 14

When comparing a rapid and slow progressing disease screening patients at a certain time and calculating a mean gives an impression of longer average survival time