2
Calculating a Rate
In New Jersey, 400 people died of tuberculosis
between January 1, 2005 and December 1,
2005.
In 2003, NJ had 1.2 million residents.
Calculate the death rate from TB in 2005.
Death rate = 400 TB deaths in 2005
1,200,000 people in 2005
Death rate = 0.0003 TB deaths/person
in 2005
Calculating a Rate
Death rate = 0.0003 deaths/person in 2005
Does this make sense???
Put the rate in perspective – multiply by a
power of 10!
Rate = 400 deaths in 2005
* 10,000
1,200,000 people
Rate = 3 deaths per 10,000 people in 2005
Interpreting a Rate
Rate:
3 deaths per 10,000 people in 2003
What does this mean?
For every 10,000 people living in New
Jersey in 2003, there were 3 deaths from
TB.
Rates
Rates can be expressed in any form that is
convenient
o
Per 100
o
Per 1,000
o
Per 10,000
o
Per 100,000
o
Per 1,000,000
In other words, the following are
equivalent:
o
0.03 per 100
o
0.3 per 1,000
o
30 per 10,000
o
300 per 100,000
Morbidity
Describes illness in a population
Two main measures of morbidity
o
Incidence
o
Prevalence
Incidence
Measures the number of
new
cases relative
to the population at risk
Incidence describes how quickly (or slowly)
new cases of disease develop over a period
of time
Incidence
=
# new cases over time
total population at risk*
*Because populations are dynamic, use the
midpoint population for the period of
interest.