# zepid.calc.utils.incidence_rate_ratio¶

zepid.calc.utils.incidence_rate_ratio(a, c, t1, t2, alpha=0.05)

Calculates the incidence rate ratio and confidence intervals from count data

Incidence rate ratio is calculated from

$IR = \frac{a}{t_1} / \frac{c}{t_2}$

Incidence rate ratio standard error is

$SE = \left(\frac{1}{a} + \frac{1}{c}\right)^{\frac{1}{2}}$
Parameters: a (integer, float) – Count of exposed individuals with outcome c (integer, float) – Count of unexposed individuals with outcome t1 (integer, float) – Person-time contributed by those who were exposed t2 (integer, float) – Person-time contributed by those who were unexposed alpha (float, optional) – Alpha value to calculate two-sided Wald confidence intervals. Default is 95% confidence interval Tuple of IR, lower CL, upper CL, SE tuple

Examples

Estimate the incidence rate ratio, standard error, and confidence intervals

>>> from zepid.calc import incidence_rate_ratio
>>> ir = incidence_rate_ratio(45, 21, 109, 158)


Extracting the estimated incidence rate ratio

>>> ir.point_estimate


Extracting the lower and upper confidence intervals, respectively

>>> ir.lower_bound
>>> ir.upper_bound


Extracting the standard error

>>> ir.standard_error