Screening

Question 1

Length-time bias

Answer 1

Screening is better at detecting disease that develops slowly. Disease that develops slowly means that you live for longer.

However, useless screening can appear to increase survival time by detecting a disease that develops more slowly but does not actually result in longer life. A disease detected by screening is likely to have a better prognosis even if it results in no difference in treatment.

Question 2

Lead-time bias

Answer 2

Useless screening can appear to increase survival time post-diagnosis by detecting a disease earlier but not actually resulting in longer life

Question 3

Healthy screenee bias

Answer 3

People who choose to attend screening tend to be healthier than those that dont

People who do not take up invitations to screen are more likely to be smokers, drinkers, have a low income, poor diet, existing medical conditions

Therefore comparisons between self-selected screened and unscreened groups are biased.

Question 4

Common types of bias in screening

Answer 4

Healthy screenee

Length-time effect

Lead-time effect

Overdiagnosis

Question 5

What is the wilson and junger critera?

Answer 5

1. The condition should be an important health problem.
2. There should be a treatment for the condition.
3. Facilities for diagnosis and treatment should be available.
4. There should be a test or examination for the condition.
5. The test should be acceptable to the population.
6. There should be an agreed policy on whom to treat.

Question 6

Overdiagnosis

Answer 6

Correct diagnosis of a disease, but the diagnosis is irrelevant because the disease will never cause symptoms within the patient’s lifetime.

Detecting a disease in patients who will die of ‘natural causes’ without diagnosis of disease.

Question 7

Overtreatment

Answer 7

Unnesseary treatment which does not improve health

Question 8

What are the main drawbacks of cervical cancer screening?

Answer 8

Some lesions will regress spontaneously

Some lesions may be treated unnecessarily

Invasive cancer may arise without any evidence of progression through pre- cancerous stages

Treatment of pre-invasive lesions may have an effect on future reproductive outcomes

An abnormal smear test may cause psychological distress

Question 9

What are the three genetic screening time-points in pregnancy?

Answer 9

Pre-conception genetic screening

Anetnatal screening

New born screening