Chronic wasting disease (CWD) prevalence among harvested adult male mule deer (Odocoileus hemionus) in the 36 western Canadian or US management units estimated at the beginning of the unit's respective analysis period (2002–06). Visual inspection revealed a clear break separating 32 units with starting prevalence ≤5% from four units with starting prevalence ≥11%. AB=Alberta, Canada; CO=Colorado; NE=Nebraska; UT=Utah; WY=Wyoming.