Multi-Factor Curve Analysis for Grouped Data in 'R' // Implements multi-factor curve analysis for grouped data in 'R', replicating and extending the functionality of the the 'Stata' ado 'mfcurve' (Krhmer, 2023) https://ideas.repec.org/c/boc/bocode/s459224.html. Related to the idea of specification curve analysis (Simonsohn, Simmons, and Nelson, 2020) doi:10.1038/s41562-020-0912-z. Includes data preprocessing, statistical testing, and visualization of results with confidence intervals.