test: 656 customer-months, 203 churned
logistic regression      AUC 0.757   churned among top 50: 35
decision tree            AUC 0.690   churned among top 50: 36
random forest            AUC 0.751   churned among top 50: 37
hist. gradient boosting  AUC 0.735   churned among top 50: 33
permutation importance (drop in test AUC when a column is shuffled):
  recency        +0.056
  avg_gap        +0.020
  orders_90      +0.015
  spend_90       +0.010
  tenure         +0.008
  orders_all     +0.007
  express_share  +0.004
  trend          -0.004
