In modeling memory discrimination in psychology experiments, people often recommend d-prime from Signal Detection Theory (https://en.wikipedia.org/wiki/Sensitivity_index). Other recommend simple "theory-free" discrimination scores (Hits-False Alarms). This is frustrating because all measurement designs carry theoretical distributional and metric assumptions, just because one is explicit (as in signal detection theory: d' = Z(hit rate) − Z(false alarm rate), where function Z(p), p ∈ [0,1], is the inverse of the cumulative distribution function of the Gaussian distribution.) does not mean the simple (hit rate minus false alarm rate) is theory free an unadulterated. The theoretical assumptions are just different.