An automated external defibrillator (AED) and methods for a corrective CPR prompting system. The AED includes a sensor that obtains compression measurement data of CPR chest compressions and a control system including a microprocessor programmed to run a non-parametric, Information-Theoretic analysis of the compression measurement data. The analysis includes ranking provided compression measurement data, determining a prompt time TN for review, locating the compression measurement data at TN in an initial expected histogram of depth and rate aspects of the compression data measurements with upper and lower limits, that divides the intervals of the histogram into a plurality of sections, weighting the compression measurement data based on a plurality of factors, deriving information content of the compression measurement data by mapping a probability density function into an information content function, and determining if a particular corrective prompt is necessary. The AED also includes a prompting device that provides corrective CPR.