Screening

Question 1

Function screening? Aim?

Answer 1

Sorts out those who have disease and those who don’t
Aim- prevent disease/early detection

Question 2

Explain screening:
Population based
Opportunistic
Communicable disease
Pre/employment/commercial

Answer 2

Population based- Testing entire population
Opportunistic– patient seeks help for something else and doctor takes a sample
Communicable disease– for analysing/controlling epidemics/pandemics
Pre-employment/commercial– occupational health

Question 3

What is screening test criteria named?

Answer 3

Wilson and Junger

Question 4

Explain criteria in Wilson and Junger criteria?

Answer 4

Condition- important
- recognise latent phase (early catching improve prog)
- know disease progresses- recognise natural history
Test- suitable, sensitive, specific, inexpensive
- acceptable
Treatment- effective
Cost- not overly expensive
- ongoing process improvement

Question 5

What is false positive?

Answer 5

Patient doesn’t have disease

Question 6

3 for screening?

Answer 6

1) Prevent suffering
2) Early identification beneficial
3) Early treatment cheaper

Question 7

3 against screening?

Answer 7

1) Damage caused wrong results
2) Adverse effects healthy ppl
3) Personal choice compromised

Question 8

Answer 8

Question 9

Define sensitivity?

Answer 9

Test probability of person with disease obtaining positive test result
Measure how well test picks up those with a disease

Probability of a true positive
= Number of true positive results / total number screened
= true positives / (true positives + false negatives)

Question 10

Define specificity?

Answer 10

Test probability of person without disease testing negative
Measure how well test recognises those without disease
= Number of true negatives / total number screened
= True negatives / (false positives + true negatives)

Question 11

Define incidence?

Answer 11

Number new cases per unit time
% per population size eg. per 100,000

Question 12

What increases and decreases incidence?

Answer 12

Increase- screening, identify new cases, increase risk factors
Decrease- primary prevention- reduce risk factors

Question 13

Define prevalence?

Answer 13

Number of existing cases at particular point in time
People enter prevalence pool when diagnosed with condition

Question 14

What increases and decreases prevalence?

Answer 14

Increase- screening programme (identify new cases), increase risk factor, increase LE
Decrease- cures, decrease RF

Question 15

What occurs if prevalence high (effects)?

Answer 15

Incidence false positive falls

Reverse rare disease

Question 16

State 3 types of bias?

Answer 16

Selection bias- ppl who choose participate screening may diff to those who don’t
Lead time bias- screening identifies disease earlier than before- give impression survival prolonged
Length time bias- disease longer presentation more likely detected by screening than those more aggressive

Question 17

What is positive predictive value?

Answer 17

Proportion ppl with positive test who actually have disease

True positives / (true positives + false positives)

Question 18

What is negative predictive value?

Answer 18

Proportion ppl without disease who correctly excluded by screening test

True positives / (false negatives + true negatives)