Lecture 2, part 4

Question 1

What’s the denominator of prevalence?

Answer 1

Total population

Question 2

What is a major use of prevalence?

Answer 2

Resource planning

Question 3

Advantages of prevalence

Answer 3

Measures the overall burden of dz
Useful for chronic dzs which have long duration and difficult to pinpoint onset

Question 4

Disadvantages of prevalence

Answer 4

Based on both incidence and duration of illness
Poor choice for dzs or outcomes with short duration or high mortality rate

Question 5

Type of # of cumulative incidence

Answer 5

Proportion

Question 6

Units of cumulative incidence

Answer 6

None

Question 7

Range of cumulative incidence

Answer 7

0 to 1

Question 8

Numerator of cumulative incidence

Answer 8

New cases

Question 9

Denominator of cumulative incidence

Answer 9

Pop at risk

Question 10

Major uses of cumulative incidence

Answer 10

Research on causes, prevention, and tx of dz

Question 11

Advantages of cumulative incidence

Answer 11

Measures the risk or probability of developing the dz during the study period
Easy measure for ppl to understand

Question 12

Disadvantages of cumulative incidence

Answer 12

Less accurate than true rate
Risk can change over time, so selection of appropriate time period is important
Works better for fixed pops

Question 13

Type of number for incidence rate

Answer 13

True rate

Question 14

Units of incidence rate

Answer 14

1/time or t-1

Question 15

Range of incidence rate

Answer 15

0 to infinity

Question 16

Numerator of incidence rate

Answer 16

New cases

Question 17

Denominator of incidence rate

Answer 17

Person-time at risk

Question 18

Major uses of incidence rate

Answer 18

Research on causes, prevention, and tx of dz

Question 19

Advantages of incidence rate

Answer 19

Conveys the speed at which new cases occur
Person-time can accommodate persons joining/leaving the study
Good for transient, dynamic pops

Question 20

Disadvantages of incidence rate

Answer 20

Assumes that probability or risk of dz during the study period is constant
Difficult to calculate (can use mid-year pop for denominator)
Difficult to understand

Question 21

Prevalence formula in relation to incidence

Answer 21

Prevalence = incidence x duration of dz
P / (1-P) = IR x d
P = proportion of total pop with the dz
1- P is the proportion of the total pop without the dz
d = avg duration of dz
When dz occurrence is rare, simplifies to P = IR x d

Question 22

When does prevalence increase?

Answer 22

New cases are added to the existing cases

Question 23

When does prevalence decrease?

Answer 23

People are cured, recover, or die

Question 24

Possible interpretations for changes in incidence

Answer 24

Change in case definition or dz detection
Selective migration or pop changes
Change in prevention/intervention strategy
Introduction of a new risk factor
Change in habits/behaviors
Change in dz virulence/transmissibility

Question 25

Possible interpretations for changes in prevalence

Answer 25

Change in case definition or dz detection
Selective migration or pop changes
Change in prevention/intervention strategy
Change in the incidence of dz
Change in the duration of dz