HC.5: Occurence / frequency

Question 1

Measures of frequency

Answer 1

How often does disease occur
- Prevalence
- Cumulative incidence
- Incidence rate

Question 2

Measures of association

Answer 2

How to compare disease occurence
- Relative risk
- Risk difference

Question 3

Prevalence

Answer 3

Prevalence = existing cases / total population
- Proportion/fraction/percentage
- Ranges from 0 to 1 (or 100%)
- Prevalence rate

Question 4

Cumulative incidence

Answer 4

CI(dt) = new cases / N(t=0)
- Proportion/fraction/percentage
- Ranges from 0 to 1 (or 100%)
- Time specification
- Define population at risk
- Complete follow-up

Question 5

Cumulative incidence in medicine

Answer 5

• Absolute risk
• Case fatality, lethality
• 5-years survival
• Attack rate
• Life-time risk

Question 6

Incidence rate

Answer 6

Incidence rate = new events/population-time
- Density, not proportion
- Unit in person-years
- Range from 0 to >1
- Life-expectancy = 1 / incidence rate

Question 7

Relation between IR and prevalence

Answer 7

Prevalence = IR x duration of disease

Question 8

Relative risk

Answer 8

Risk(1) / Risk(0) = CI(1) / CI(0)
- Ranges from 0 to infinity
- Null valuea = 1
- Long follouw-up: CIR approaches 1

Question 9

Risk difference

Answer 9

Risk difference = CI(1) - CI(0)