Field Notes
Choosing sampling depth for mid-size procurement books
Sampling depth is the question every scoping call circles back to. Test too little and stakeholders doubt the work; test everything and the engagement becomes a second accounts-payable department.
For books in the mid-size range we usually stratify: high-value invoices get near-full coverage, medium bands get statistical samples, and low-value high-volume lines get focused spot checks on known risk categories such as freight, temporary labour, and marketing retainers.
Document readiness matters more than raw count. Fifty clean invoice packets with matching POs and receipts teach more than two hundred incomplete scans. We price and schedule on the assumption that your team can retrieve packets within five business days of our request list.
Bring your last external auditor’s sample sizes to the scoping call if you have them. Aligning our depth with that baseline makes the findings easier to defend when the same questions return later in the year.