Measures of disease frequency

Question 1

prevalence

Answer 1

at a specific point in time

proportion of people with diseaes

Question 2

incidence

Answer 2

over a period of time

proportion of new cases of a disease (taking into account at risk but initially disease free individuals)

Question 3

two types of incidence

Answer 3

cumulative incidence

incidence rate

Question 4

If it only gives __% and __ per 10,000 people , whats the cumulative incidence and the incidence rate?

Answer 4

cumulative incidence: __%

incidence rate: __ per 10,000 people

Question 5

if person years are given, define cumulative incidence and incidence rate

Answer 5

over a set period of time, for at risk yet disease free individuals

• cumulative: new cases/all initial people
• incidence rate: new cases/person-time days

Question 6

how to calculate person time days?

Answer 6

for all people at risk, sum of the days that they’re disease free. loss to follow up is not included.

Question 7

say you have two diseases (A and B) with the same incidence (rate of new cases) but disease A lasts twice as long as B. what does this mean in terms of prevalence

Answer 7

prevalence involves picking a random point in time, and measuring prop of disease

therefore, two times more likely to select A - so prevalence of A is twice that of B

Question 8

formula - based on incidence, prevalence and duration of disease

Answer 8

prevalence / duration = incidence

Question 9

what conditions are required for this definition to hold

Answer 9

prevalence is small

pop is stationary

Question 10

using this formula:

• short duration/acute diseases have a ____ prevalence and ____ incidence
• long duration/chronic diseases have a ____ prevalence and ____ incidence

Answer 10

low, high

high, low