Week 3 - Measuring Disease in Populations

Question 1

Prevalence (point)

Answer 1

The number of sufferers divided by the number at risk: proportion of population who are affected by the disease.

Question 2

What is prevalence influenced by?

Answer 2

1. Incidence: increased incidence –> increased prevalence
2. Death –> increased deaths –> reduced prevalence
3. Cure –> increased cure –> reduced prevalence

Question 3

What is the importance of systematic variation between groups?

Answer 3

1. Gives clues to the causes of disease

2. Decide whether treatments work or not

Question 4

Age-sex standardisation

Answer 4

1. Calculate a age-specific mortality rate ratio for each 5 year age band
2. Single overall rate ratio which takes account of systematic variation
3. Summary figure describing the mortality experience of a local population compared with a standard reference population, which takes account of the confounding influences of age and sex

Question 5

Incidence rate

Answer 5

Dividing the number of new cases observed (events) by the number of person-years; it gives us a measure of average individual risk.

Question 6

Why are age and sex strong determinants of the need for services?

Answer 6

• Immunisations are largely confined to children, obstetric services are only used by women, usually aged between 15-44 years;
• Knowledge of the age-sex breakdown is essential to plan which services are needed; it allows forecasting of future populations - knowledge of how the age-sex profile will change will allow tailoring of future services to meet predicted changes in health needs