From SAB 99:

"...Materiality concerns the significance of an item to users of a registrant's financial statements. A matter is "material" if there is a substantial likelihood that a reasonable person would consider it important. In its Statement of Financial Accounting Concepts No. 2, the FASB stated the essence of the concept of materiality as follows:

The omission or misstatement of an item in a financial report is material if, in the light of surrounding circumstances, the magnitude of the item is such that it is probable that the judgment of a reasonable person relying upon the report would have been changed or influenced by the inclusion or correction of the item.3

This formulation in the accounting literature is in substance identical to the formulation used by the courts in interpreting the federal securities laws. The Supreme Court has held that a fact is material if there is –

a substantial likelihood that the . . . fact would have been viewed by the reasonable investor as having significantly altered the "total mix" of information made available. 4

Under the governing principles, an assessment of materiality requires that one views the facts in the context of the "surrounding circumstances," as the accounting literature puts it, or the "total mix" of information, in the words of the Supreme Court. In the context of a misstatement of a financial statement item, while the "total mix" includes the size in numerical or percentage terms of the misstatement, it also includes the factual context in which the user of financial statements would view the financial statement item. The shorthand in the accounting and auditing literature for this analysis is that financial management and the auditor must consider both "quantitative" and "qualitative" factors in assessing an item's materiality.5 Court decisions, Commission rules and enforcement actions, and accounting and auditing literature6 have all considered "qualitative" factors in various contexts."