zepid.calc.utils.risk_difference¶
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zepid.calc.utils.risk_difference(a, b, c, d, alpha=0.05)¶ Calculates the risk difference and confidence intervals from count data.
Risk difference is calculated as
\[RD = \frac{a}{a + b} - \frac{c}{c + d}\]Risk difference standard error is calculated as
\[SE = \left(\frac{R_1 \times (1 - R_1)}{a+b} + \frac{R_0 \times (1-R_0)}{c+d}\right)^{\frac{1}{2}}\]Parameters: - a (integer, float) – Count of exposed individuals with outcome
- b (integer, float) – Count of unexposed individuals with outcome
- c (integer, float) – Count of exposed individuals without outcome
- d (integer, float) – Count of unexposed individuals without outcome
- alpha (float, optional) – Alpha value to calculate two-sided Wald confidence intervals. Default is 95% confidence interval
Returns: Tuple of risk difference, lower CL, upper CL, SE
Return type: tuple
Examples
Estimate the risk difference, standard error, and confidence intervals
>>> from zepid.calc import risk_difference >>> rd = risk_difference(45, 55, 21, 79)
Extracting the estimated risk difference
>>> rd.point_estimate
Extracting the lower and upper confidence intervals, respectively
>>> rd.lower_bound >>> rd.upper_bound
Extracting the standard error
>>> rd.standard_error