2. Measuring and Monitoring Population Health II

Question 1

Mean

Answer 1

Average value of a set of numbers

A mean’s measure of variability is its standard deviation

Question 2

Standard deviation

Answer 2

Quantifies the amount of variation in a set of values (i.e., how wide they spread across a distribution)

The further away from 0 the SD is, the more variation there is. An SD of 0 indicates that all values are close to the mean

95% of all values in a normal distribution will lie within ± 2 SD of the mean

Question 3

Prevalence and incidence are…?

Answer 3

Two of the most used measures of the frequency of health events, risk factors, and conditions

Question 4

Prevalence

Answer 4

Proportion of people experiencing certain conditions or health events (in a specified population at a given point in time)

= [Count of events of people with particular characteristic]/[Total number in the population]

Question 5

Incidence

Answer 5

Quantity of people who developed the problem/characteristic (or died) over a specific period of time (i.e., number of new cases that developed (not the number of existing cases) over a period of time)

Two methods of expressing incidence:
- 1. Cumulative incidence
- 2. Incidence rate

Question 6

What is the difference between cumulative incidence and incidence rate?

Answer 6

The difference between cumulative incidence and incidence rate is in the expression of the denominator (population at risk)

Question 7

Cumulative Incidence

Answer 7

The proportion of people who are initially free of disease but develop the disease within a specified period of time, over the initial population at risk

Serves to answer the question, “how far has the disease spread during a specified period of time?”

= [Number of new cases]/[initial population, “at risk,”] over a specified time period

Question 8

A measure of cumulative incidence assumes that…?

Answer 8

1. The initial population at risk does not change over time (e.g., the population does not increase)
2. Everyone in the initial population at risk (i.e, patient population each year) has been followed for the same period of time

These assumptions are rarely true in reality

Question 9

Incidence rate

Answer 9

The number of new cases developing during a specific period of time divided by the total disease-free person-time of observation seen in the population at risk (i.e., measures how fast a disease is spreading)

= [Number of new cases]/[Total observation time of population at risk]

People typically move in and out of populations, so incidence rate records the amount of time people in the population have been, “observed”