Screening

Question 1

Why is screening done?

Answer 1

Identify apparently healthy individuals that may be at risk of a disease/condition

Those identified offered further tests

Question 2

NHS screening programmes?

Answer 2

Bowel cancer 60-74 every 2 yrs
Breast cancer 47-73 every 3 yrs
Cervical screening 25-49 (3yrs) 50-64 (2yrs)
AAA screening men over 65 once

Fetal anomaly screen
Newborn blood spot
Newborn hearing

Question 3

What’s the criteria for screening?

Answer 3

Wilson Junger criteria (10 philosophies)

1. knowledge of disease
   - is it important condition
   - able to recognise early latent phase of disease
   - natural history understood
2. Knowledge of test
   - suitable test
   - acceptable test
   - continuous case finding
3. Treatment
   - accepted treatment
   - facilities for diagnosis
   - agreed policy on who to treat
4. Cost consideration
   - cost effective

Question 4

Draw out the screening table (looking at false/true positives/negatives)

Answer 4

Test +ve or -ve VS diagnosis +ve or -ve

Question 5

How do you calculate:

• absolute risk
• absolute risk reduction
• relative risk
• relative risk reduction
• attributable risk
• NNT

Answer 5

Absolute risk = incidence per a number (e.g 3 in 100)

Absolute risk reduction = AR of unexposed - AR exposed

Relative risk = incidence in exposed / incidence in unexposed

Relative risk reduction = ARR / AR unexposed
ALSO = 1 - RR

Attributable risk = incidence in exposed - incidence in unexposed (result X in 100 of exposed population)

NNT = 1/attributable risk

Question 6

What are confounders?

Draw a diagram.

Answer 6

Risk factors, other than those being studies, that influence the outcome

Confounder –> outcome
Confounder –> exposure

Slide 36 of 24.10 public health

Question 7

What can cause associations when there’s no actual link, other than confounding variable?

Answer 7

BIAS

Selection bias: who’s involved in the trial

Information bias: measurement, observer, recall, reporting bias

Publication bias: some trials more likely to be published than others

Question 8

Define bias?

What are the types?

Answer 8

Systematic error that results in deviation from the true effect of an exposure on an outcome

SIP (Obama)
Selection
Information
Publication

Question 9

What types of studies are there?

Answer 9

Cross sectional
Case control
Cohort
RCT

Question 10

Cross sectional study?

Answer 10

Snapshot of data of those with and without disease

To find associations at a single point in time

Question 11

Case control study?

Answer 11

Retrospective observational study which looks at a certain exposure

Get a group of people with heart disease and a group without, and look back to see whether they smoked

Question 12

Cohort study?

Answer 12

Longitudinal prospective study which takes a population of people and records their exposures and conditions they develop

Question 13

RCT?

Answer 13

Similar participants randomly allocated to intervention or control groups to study the effect of the intervention

Question 14

Rank the types of studies order of reliability?

Answer 14

Systematic review / meta analysis
RCT
Cohort
Case control
Cross sectional

Question 15

How would you assess causality?

Answer 15

Bradford Hill criteria

1. Strength of association (magnitude of relative risk)
2. Dose-response (higher exposure, higher risk)
3. Consistency (in other studies)
4. Reversibility (removal of exposure reduces risk of disease)
5. Biological plausibility
6. Coherence

Question 16

Reverse causality?

Answer 16

Refers to situation when outcome is causing the exposure rather than exposure causing outcome