MEASURES OF MORBIDITY
Review Questions:
What is the purpose of surveillance?
o To monitor disease, illness, and injury for changes in disease and/or risk-factor frequency
What is the difference between active and passive surveillance?
o Active = health jurisdiction generates/gathers data themselves. Expensive, harder to
develop, but more accurate.
o Passive = health jurisdiction receives data generated by other sources. Inexpensive, easy
to develop, but less accurate.
Define Incidence?
o Number of new cases, during a specified period of time, in a population at risk
Measure of event, measure of risk
o Number of new cases of disease occurring in the population during a specified period of
time DIVIDED BY number of persons who are at risk of developing disease during that
period of time TIMES 10n
Rule of thumb is to use the smallest multiplier of 10 that gets you one number
to the left of the decimal, that is at least 1000 or larger.
Objectives
Define prevalence and discuss its use in epidemiology
Discuss issues that impact accurate incidence and prevalence statistics
Discuss the relationship between incidence and prevalence
Prevalence
The proportion of people in a population affected by a disease
o Point prevalence (current)
Most often talked about
o Period Prevalence (over a period of time)
Measures the burden of disease
o Impact of health problem;
Morbidity and Mortality
Financial cost
Other indicators; QALYs, DALYs
Calculation:
o Number of cases of disease present in the population at a specified period of time /
number of persons in the population at that time
o X 10n (most often 100)
o The denominator can ONLY contain people who are a part of that population
Lets Practice: Point Prevalence
We reviewed the medical records of all the current patients at a large urban hospital;
o There were 3,465 patients between 60-74
974 cases of osteoporosis were identified
What is the Point PR for osteoporosis in this group?
o Divide the cases of illness by the total population:
,465 = 0.2811
o Multiply the answer by 100:
0.2811 x 100 = 28.11
o Express it as a proportion
Review Questions:
What is the purpose of surveillance?
o To monitor disease, illness, and injury for changes in disease and/or risk-factor frequency
What is the difference between active and passive surveillance?
o Active = health jurisdiction generates/gathers data themselves. Expensive, harder to
develop, but more accurate.
o Passive = health jurisdiction receives data generated by other sources. Inexpensive, easy
to develop, but less accurate.
Define Incidence?
o Number of new cases, during a specified period of time, in a population at risk
Measure of event, measure of risk
o Number of new cases of disease occurring in the population during a specified period of
time DIVIDED BY number of persons who are at risk of developing disease during that
period of time TIMES 10n
Rule of thumb is to use the smallest multiplier of 10 that gets you one number
to the left of the decimal, that is at least 1000 or larger.
Objectives
Define prevalence and discuss its use in epidemiology
Discuss issues that impact accurate incidence and prevalence statistics
Discuss the relationship between incidence and prevalence
Prevalence
The proportion of people in a population affected by a disease
o Point prevalence (current)
Most often talked about
o Period Prevalence (over a period of time)
Measures the burden of disease
o Impact of health problem;
Morbidity and Mortality
Financial cost
Other indicators; QALYs, DALYs
Calculation:
o Number of cases of disease present in the population at a specified period of time /
number of persons in the population at that time
o X 10n (most often 100)
o The denominator can ONLY contain people who are a part of that population
Lets Practice: Point Prevalence
We reviewed the medical records of all the current patients at a large urban hospital;
o There were 3,465 patients between 60-74
974 cases of osteoporosis were identified
What is the Point PR for osteoporosis in this group?
o Divide the cases of illness by the total population:
,465 = 0.2811
o Multiply the answer by 100:
0.2811 x 100 = 28.11
o Express it as a proportion
