Public Health

Question 1

Incidence

Answer 1

The number of individuals who develop a condition in a given period of time

Units: % or per 1000

Incidence= No. of new cases during time t/ population at risk

Question 2

Prevalence

Answer 2

The number of individuals who have a condition at a particular time

Prevalence= No. of existing cases at time t/ total population size

Question 3

Absolute risk

Answer 3

The risk of developing a condition over a given time period

I.e 1 in 10 at risk of developing cancer

Question 4

Absolute risk difference

Answer 4

P of case in exposed group- P of case in unexposed group

Question 5

Relative risk

Answer 5

Ratio of risk in the exposed group to risk in unexposed group

RR= P of case in exposed group/ P of case in unexposed

Normally produces larger value than absolute risk difference

Question 6

True positive

Answer 6

Number of people who have a disease who were screened as positive

Question 7

True negative

Answer 7

Number of people who don’t have a disease who were screened as negative

Question 8

False positive

Answer 8

Number of people who don’t have a disease but were screened as positive

Question 9

False negative

Answer 9

Number of people who do have a disease but were screened as negative

Question 10

Sensitivity

Answer 10

The proportion of people with the disease who were correctly identified by the screening test

Sensitivity= True positive/ (true positive + false negative)

Question 11

Specificity

Answer 11

The proportion of people without the disease correctly identified by the screening test

Specificity= true negative/ (true negative + false positive)

Question 12

Positive predictive value

Answer 12

The proportion of people with a positive result who have the condition

PPV= True positive/ (true positive + false positive)

Question 13

Negative predictive value

Answer 13

The proportion of people with a negative result who don’t have the condition

NPV= True negative/ (true negative + false negative)

Question 14

Cross-sectional study

Answer 14

Prevalence within a population, a snapshot in time.
Exposure Outcome

+ Quick, cheap with few ethical problems and can be used to stimulate further research

• Suffers from selection bias and has no time reference

Question 15

Case-control study

Answer 15

Comparison of a group of people with a disease and a control group. Can be used to investigate risk factors.
Outcome—> Exposure

+ Quick, cheap and works well for disease with long latent periods

• selection/ information bias and can’t tell incidence

Question 16

Cohort study (longitudinal study)

Answer 16

A systematic study (follow up) of a group of people. Can be prospective and/or retrospective
Exposure—> Outcome

+multiple outcomes, can catch rare diseases, can give incidence, identifies exposure/ confounders

• expensive, time consuming and study power is lost from lack of follow up

Question 17

Randomised control trails

Answer 17

Randomised sample separated into treatment arm and control arm. Measure no. with + without disease in each.

+Gold standard, removes bias and confounders by randomisation, blinding and placebo

-Expensive, ethical issues and poor compliance reduces power

Question 18

Ecological study

Answer 18

Correlations within populations I.e link between smoking and lung cancer in different nations. Descriptive study

Question 19

Simple random sampling

Answer 19

Each member of the population has an equal chance of being selected

Question 20

Systematic sampling

Answer 20

Members of a population are selected at equal intervals

Question 21

Stratified sampling

Answer 21

Population separated into groups (strata) that should be similar. Random sampling then used within groups

Question 22

Cluster sampling

Answer 22

Population put into groups (clusters). Random sampling then used to selected whole groups

Question 23

Validity

Answer 23

Whether a study measures what it’s supposed to

Question 24

Reliability

Answer 24

Whether a study produces similar results consistently

Question 25

Standard deviation

Answer 25

Mean spread of data from the mean

Question 26

Odds ratio

Answer 26

Approximation of relative risk used in especially large samples

OR= no. With/ no. Without
Event occurs/ event doesn’t occur

Question 27

One unit of alcohol

Answer 27

8g/10ml of pure alcohol

Question 28

Primary prevention

Answer 28

Systems to prevent a disease ever occurring e.g. education, campaigns, legislations, restrictions

Question 29

Secondary prevention

Answer 29

To detect early disease and slow progression e.g. aspirin, b- blockers, screening

Question 30

Tertiary prevention

Answer 30

Once disease is established and symptomatic, tertiary prevention aims to reduce complications of severity of the disease

Question 31

High risk prevention

Answer 31

Targets highest risk individuals
Aim to reduce risk below set limit

Favours those who are more affluent and educated. They are:
More likely to engage with health services
More likely to comply with treatment
More likely to have the means to change their lifestyle

Question 32

Population approach to prevention

Answer 32

Targets all individuals
Aim to reduce the risk for each individual
Recognised that the low risk majority may contribute most cases
Concerns over treating the well

Question 33

Primary prevention in CHD

Answer 33

Lifestyle changes and management of related condition I.e hypertension, high cholesterol and diabetes

SNAP
Smoking(tax, legislation, cessation services, education)
Nutrition(recommendations, regulations, labelling, food in schools)
Alcohol (tax, alcohol pricing, regulation)
Physical activity

Medication: anti-hypertensives, statins, insulin