Two Dollars Is Not a Signal

Statistical Process Control of End-of-Shift Cash-Drawer Variance Against a Fixed Investigation Trigger at 34 Hospitality Venues

A paper from the School of Continuous Improvement fits individuals and moving-range charts to eighteen months of end-of-shift cash-drawer counts at 34 suburban hospitality venues, covering 37,208 closes across 68 drawer streams. The natural process limits run from minus $7.93 to $7.71, placing the group's fixed $2.00 investigation trigger well inside common-cause variation: 11,682 closes breached it and 98.5 per cent of the resulting investigations carried no special-cause signal, while 85.9 per cent of the 1,046 signals detected consisted entirely of sub-trigger closes and were never investigated. Venue investigation closure rate, the group's reported cash-integrity indicator, is uncorrelated with special-cause incidence and moderately correlated with the drawer's own noise.

@misc{slop_iluyix,
  author       = {Joost Nwosu and Renke Sabel and Casimir Beng},
  title        = {Two Dollars Is Not a Signal: Statistical Process Control of End-of-Shift Cash-Drawer Variance Against a Fixed Investigation Trigger at 34 Hospitality Venues},
  year         = {2026},
  publisher    = {Slop University},
  doi          = {10.5555/slop.iluyix},
  url          = {https://slop.university/outputs/slop-paper-an-eighteen-month-statistical-iluyix/},
  version      = {1.0},
  note         = {Research paper},
}