Measures of Morbidity

Question 1

Incidence

Answer 1

o ¨Number of new cases of disease that occur in a population at risk over time

Question 2

Cumulative Incidence

Answer 2

• ¨When a group of people are all observed over some time period
• ¨Technically not a rate and better talked about as a risk or incidence proportion
• (# of new cases/pop. at risk)* constant per specified time period

Question 3

Person-time Incidence Rate

Answer 3

• ¨Used when a group of people are observed over different amounts of time
• ¨This is a true rate and talks to the speed of developing disease
• (# of new cases/person-time at risk) * constant

Question 4

Prevalence

Answer 4

o (# of new and old cases/ pop. at risk)

Question 5

Point Prevalence

Answer 5

• ¨The proportion of the population that is affected by the disease at a point in time (aka ‘snapshot’)

Question 6

Limitations of Incidence and Prevalence

Answer 6

o	¨Numerator
        -Is it complete?
        -Is it accurate?
o	¨Denominator
        -How do you define who is at risk?
        -Is it complete?
        -Is it accurate?

Question 7

Crude

Answer 7

• single number, good for capturing the bigger picture
• general pop.
• average rate
• does NOT account for differences in certain factors

Question 8

Specific

Answer 8

• ways in which we subset/stratify our population groups (age and sex and etc… specific rates)
• both numerator and denominator specific for the factor being studied
• might now know which characteristics you are looking for
• So MANY specific rates– too congested, if numerators get small—small rate if denominator is huge, imprecise, unstable estimate, less random variation (larger numerator—more stable)

Question 9

Adjustment

Answer 9

• Everything is consolidated into a SINGLE number, statistical tool to distinguish and compensate for difference (remove effect of a particular factor) in groups that will be compared

Question 10

Attack Rate/Ratio

Answer 10

o ¨Used to describe outbreaks
o ¨Tells us the proportion of persons exposed who fall sick
o ¨Usually the time dimension is implied as the duration of the outbreak
o (# of new cases/ # of people exposed)

Question 11

Mortality Rate

Answer 11

o ¨A measure of the incidence of death

o (# of deaths/ [# of persons in population—generally use a midyear estimate)* constant per specified time period

Question 12

Cause-specific Mortality Rate

Answer 12

o ¨A measure of the rate of death from a certain cause
o (# of deaths due to specific cause / [# of persons in the pop. –use mid-year estimate])* constant per specified time period

Question 13

Case-specific Mortality Rate

Answer 13

o ¨Tells us the risk of death among diagnosed cases
o ¨An indicator of the severity of disease
o (# of deaths from disease / # of people with disease) * constant per specified time period

Question 14

Proportionate Mortality

Answer 14

o ¨Measure of the relative importance of a specific cause of death in relation to all deaths
o ¨NOT a risk or rate
o ¨Can be misleading
o (# of deaths due to a specific cause / # of total deaths)
-denominator is NOT people who are at risk
-value is dependent on the number of deaths
o if other cause-specific deaths increase—proportion changes and your cause of death does NOT play into that CHANGE in proportion