np Chart — Invoice Error Count
Twenty-four weeks of errors found in a constant audit sample of 200 invoices, plotted as counts rather than proportions, with binomial limits around np̄ = 8.79 and a rule-5 signal as the new billing rules bed in.
Make it your own.
title "Invoice errors — weekly audit sample"
chart np
unit "errors per 200 invoices"
labels: W1, W2, W3, W4, W5, W6, W7, W8, W9, W10, W11, W12, W13, W14, W15, W16, W17, W18, W19, W20, W21, W22, W23, W24
# Constant sample size, so the raw count is plotted directly — an np
# chart says "nine invoices were wrong", which an auditor can act on.
sample n: 200 defects: 9
sample n: 200 defects: 9
sample n: 200 defects: 8
sample n: 200 defects: 6
sample n: 200 defects: 4
sample n: 200 defects: 5
sample n: 200 defects: 12
sample n: 200 defects: 5
sample n: 200 defects: 7
sample n: 200 defects: 7
sample n: 200 defects: 11
sample n: 200 defects: 10
sample n: 200 defects: 8
sample n: 200 defects: 5
sample n: 200 defects: 6
sample n: 200 defects: 11
sample n: 200 defects: 7
sample n: 200 defects: 4
# New multi-currency billing rules go live in week 19.
sample n: 200 defects: 13
sample n: 200 defects: 12
sample n: 200 defects: 11
sample n: 200 defects: 15
sample n: 200 defects: 11
sample n: 200 defects: 15