Inclusion Analysis

Inclusion analysis is the name given by Operis to a black box testing technique that it has found to make the checking of key financial ratios calculated by spreadsheet models quicker, easier and more likely to find omission errors than code inspection. 1 CALCULATE MORE THAN ONCE One approach among many [Pryor, 2004] [Panko, 2006] for improving the chance that a spreadsheet delivers the results that it is intended to deliver is to calculate quantities two or more different ways [Ettema et al, 2001]. If independent methods produce identical answers, there is a good chance, though no guarantee, that those answers are trustworthy. If the answers are not identical, the act of reconciling them and fathoming out what is causing the difference is often illuminating, not just about what mistake has been made, but about the underlying problem addressed by the spreadsheet and the assumptions being made in solving it. Calculating a result by an alternative method is a standard weapon of a spreadsheet auditor. Most of the recent development focus of the Operis Analysis Kit [Oak, 2010], a software application for developing and reviewing spreadsheets public by the author’s own company Operis, has been directed at accelerating the production of parallel reconstructions and of identifying where and why they have diverged from the original model. At least one of the large international accountancy practices declines to perform spreadsheet audits [Croll, 2003], or does so only grudgingly, preferring to reconstruct the spreadsheet and reconcile the outputs. This process no doubt delivers outstanding results, but not every client values them enough to pay five times as much for them. Spreadsheet developers don’t have to wait for an outside auditor to subject their spreadsheet to parallel reconstruction. They can calculate results repeatedly themselves, in their own spreadsheet. An obvious example concerns a table of numbers.