This last point is worthy of further explanation. Because of the way some organizations account for their liabilities, they may be unable to respond to requests for confirmation. For example, government agencies and large industrial organizations often use an open-invoice system for liabilities. Under this approach, invoices are recorded individually rather than being summarized or grouped by creditor. In this environment, no accounts payable subsidiary ledger exists. Each invoice is paid (closed) as it comes due. For financial reporting purposes, total accounts payable is calculated simply by summing the open (unpaid) invoices. Determining the liability due to a particular creditor, which may consist of multiple open invoices, is not such a simple task. The auditor should not assume that an organization using this approach would invest the time needed to respond to the confirmation request. Under such circumstances, the confirmation process would be ineffective.