Preventative Medicine

Question 1

What are the 3 categories of prevention?

Answer 1

Primary - preventing onset of disease e.g. immunisation

Secondary - halt progression of disease e.g. early diagnosis/screening

Tertiary - limit disability/complications in established disease e.g. rehabilitation

Question 2

Describe: Geoffrey Rose’s single population theory

Answer 2

• Population-wide prevention - shift the mean of the entire distribution to the left to accommodate for the low-risk people
• Identify + treat the top end of the population distribution

Question 3

Describe Geoffrey Rose’s single population theory with the example of preventing MIs

Answer 3

• Shift the distribution to the left to reduce everyone’s blood pressure - do this by reducing obesity and salt in diet
• Target the high-risk subjects - screening in GPs

Question 4

Describe: individual-based intervention

Answer 4

1. Identify individuals at high risk with screening
2. Intervene only in individuals at high risk
3. Risk-benefit balance assessed individually

Question 5

Describe: population-based intervention

Answer 5

1. Identify important risk factors for the community (prevalence)
2. Policy to reduce risk factor irrespective of individual risk
3. Risk-benefit balance for whole community

Question 6

Define: sensitivity

Answer 6

The proportion of people with the disease who are identified as having it by a positive test

= a/(a+c)

Question 7

Define: specificity

Answer 7

The proportion of people without the disease who are correctly re-assured by a negative test result

= d/(d+b)

Question 8

Define: positive predictive value

Answer 8

The probability that a person with a positive test result actually has the disease

= a/(a+b)

Question 9

Define: negative predictive value

Answer 9

The probability that a person with a negative test result doesn’t have the disease

= d/(c+d)

Question 10

Describe: high sensitivity

Answer 10

• Maximises identification of diseased people in the screened population
• Relatively few false negatives
• Unnecessary investigations/treatments for others
• Lots of false positives

Question 11

Why would high sensitivity be desirable?

Answer 11

• Adverse consequences of missed diagnosis for the individual might be significantly worse than early diagnosis
• Serious communicable diseases in society
• Correct diagnosis given before treatment started

Question 12

Describe: high specificity

Answer 12

• Detects only people with the disease
• Relatively few false positives
• Will miss some people who have/are at risk of disease
• Lots of false negatives

Question 13

Why would high specificity be desirable?

Answer 13

• Diagnosis is associated with anxiety/stigma
• Further investigations are time-consuming/painful
• Cases are likely to be detected by other means before it is ‘too late’ for effective treatment
• Treatment is to be offered without further investigations

Question 14

Define: lead time bias

Answer 14

Early diagnosis falsely appears to prolong survival

In reality, it only identifies the disease early rather than increasing survival

Question 15

Define: length time bias

Answer 15

Screening over-represents less aggressive disease (people with more severe miss the screening may be through death)

This makes the screening look better

Question 16

What are the 10 principles for screening for disease laid out by Wilson and Jungner?

Answer 16

• The condition sought should be an important problem
• There should be an acceptable treatment for patients with the recognised disease
• Facilities for diagnosis and treatment should be available
• There should be a recognised latent or early symptomatic stage
• The natural history of the condition should be adequately understood
• There should be a suitable test or examination
• The test or examination should be acceptable to the population
• There should be agreed policy on whom to treat as patients
• The cost of case-finding should be economically balanced in relation to the possible expenditure
• Case finding should a continuous process and not a ‘once and for all’ project

Question 17

Define: case fatality rate

Answer 17

Number of people who die from the disease/number of people with disease

Question 18

Define: mortality rate

Answer 18

Number of people who die from disease/number of people who die

Question 19

Define: risk

Answer 19

Number of new cases/number at risk

Question 20

Relative risk = 1

Answer 20

The risk in the exposed group is the same as the risk in the unexposed group

Question 21

Relative risk < 1

Answer 21

The exposure is associated with a protective effect

Question 22

Relative risk > 1

Answer 22

The exposure is associated with harm

Question 23

Define: odds ratio

Answer 23

(Those with the disease and exposed to risk factor x Those without disease and not exposed) / (Those with the disease and not exposed x Those without the disease and exposed)

Question 24

Odds ratio = 1

Answer 24

The probability of an event occurring is the same as the probability that the event does not occur

Question 25

What qualities must a hypothesis have?

Answer 25

• Plausible
• Falsifiable (able to be accepted/rejected)
• Have direction
• Be precise