# zepid.calc.utils.incidence_rate_difference¶

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

Calculates the incidence rate difference and confidence intervals from count data

Incidence rate difference is calculated from

$ID = \frac{a}{t_1} - \frac{c}{t_2}$

Incidence rate difference standard error is

$SE = \left(\frac{a}{t_1^2} + \frac{c}{t_2^2}\right)^{\frac{1}{2}}$
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 ID, lower CL, upper CL, SE) tuple

Examples

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

>>> from zepid.calc import incidence_rate_difference
>>> ird = incidence_rate_difference(45, 21, 109, 158)


Extracting the estimated incidence rate ratio

>>> ird.point_estimate


Extracting the lower and upper confidence intervals, respectively

>>> ird.lower_bound
>>> ird.upper_bound


Extracting the standard error

>>> ird.standard_error