Estimate Potential Impact and Population Attributable Fractions with Aggregated Data // Uses the delta-method to estimate the Potential Impact Fraction (PIF) and the Population Attributable Fraction (PAF) from summary data. It creates point-estimates, confidence intervals, and estimates of the variance. Provides an extension to the aggregated data method in Chan, Zepeda- Tello et al (2025) doi:10.1002/sim.70214.