C.I. Calculator: Single Incidence Rate


Data Input: (Help) (Example)

Input

 

Result

1-\

Rate

a

Lower

N

 

Upper

 

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:

  1. Enter

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

  1. Click the button Calculate to obtain the lower and upper endpoints of 100(1-\)% confidence interval
  1. Click the button Reset for another new calculation


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




Example

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)

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