Note:
Variables |
Descriptions |
1-£\ |
Two-sided confidence level |
a |
Number of clinical events |
N |
Person-time at risk |
Rate |
Incidence rate |
Lower |
Lower C.I. |
Upper |
Upper C.I. |
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Description:
Incidence rate is the rate at which new clinical events occur in a population.
It is the number of new events divided by the population at risk of an event in a specific time period, sometimes it is the person-time at risk.
Procedure:
a) Value of 1-£\, the two-sided confidence level
b) Value of a, the number of clinical events
c) Value of N, the person-time at risk
Formula:
Define:
Define the standard error:
The 100(1-£\)% confidence interval is defined as:
Notation:
100(1-£\)% confidence interval: We are 100(1-£\)% sure the true value of the parameter is included in the confidence interval
: The z-value for standard normal distribution with left-tail probability
Suppose the number of new cases is 9 (a = 9)
Person-year at risk is 4028.16 (N = 4028.16)
Then the incidence rate is 0.0022343 and
The 95% confidence interval ((1-£\) =0.95) is (0.0011634, 0.004291)