changed to new test method for singificance

paper/src/chapters/03-methodology.tex

@@ -303,13 +303,9 @@ To train a robust pricing learner, we need a simulator that can generate realist
 \subsubsection{Ground-Truth Separability}
 Because sessions are collected under controlled experimental conditions where each actor is assigned a known type at the start of the trial, labels $\theta_s \in \{H, A\}$ are available as ground truth rather than as the output of a heuristic classifier. We therefore estimate separate transition kernels directly from each labeled partition $\mathcal{D}_H$ and $\mathcal{D}_A$, treating the resulting $\hat{\mathcal{T}}_H$ and $\hat{\mathcal{T}}_A$ as the ground-truth behavioral profiles for each class. We then ask a direct methodological question: are the kernels separable enough to justify downstream pricing control that depends on that separability?
 
-To answer this, we compute average KL divergence between transition probability matrices. This statistic gives global separability and event-level diagnostics at the same time. To test whether the observed between-class value exceeds finite-sample estimation noise, we compute an intra-class bootstrap baseline by repeatedly splitting $\mathcal{D}_H$ and $\mathcal{D}_A$ into two random halves, fitting a transition kernel on each half, and re-computing the same average KL statistic for each split.
+To answer this, we compute per-session KL divergence scores against both class-level centroids. For each session $s$ in either partition, we fit a session-level event transition kernel $\hat{\mathcal{T}}_s$ from that session's trajectory alone, then compute its average KL divergence to the human centroid ($\Delta_{H,s}$) and to the agent centroid ($\Delta_{A,s}$). The per-session separability score is the gap $\Delta_{H,s} - \Delta_{A,s}$: a negative value indicates proximity to human behavior, a positive value indicates proximity to agent behavior.
 
-Formally, for $B$ bootstrap splits per class we obtain reference samples $\{d_{H,b}^{\text{intra}}\}_{b=1}^B$ and $\{d_{A,b}^{\text{intra}}\}_{b=1}^B$, then compare the between-class divergence $d^{\text{inter}}$ against the pooled null distribution. We report pooled mean and variance, lift ratio $d^{\text{inter}}/\mathbb{E}[d^{\text{intra}}]$, and the empirical one-sided p-value
-\begin{equation}
-\hat p = \frac{1 + \sum_{j=1}^{2B}\mathbf{1}\{d_j^{\text{intra}} \ge d^{\text{inter}}\}}{2B + 1},
-\end{equation}
-which gives a direct significance check for separability before using divergence-derived centroid control signals in pricing.
+The normality assumption cannot be made for KL divergence distributions, which are right-skewed and bounded below by zero, so we do not use a Student's $t$-test. Instead we apply a Mann-Whitney $U$ test \parencite{mann_test_1947} on the per-session gap scores between the two groups. The Mann-Whitney test is a rank-based nonparametric test that compares the stochastic ordering of two independent samples without distributional assumptions, making it appropriate for small samples drawn from skewed populations. We report $U$, the exact two-sided $p$-value, and group-level descriptive statistics for the gap scores.
 
 \begin{definition}[Kullback-Leibler Divergence for Transition Distributions]
 Let $P_e$ and $Q_e$ be categorical distributions over destination states following event $e$, derived from human and agent trajectories respectively. The KL divergence between these distributions is: