and comparisons. 

For additional information about each line item summarized above, refer to Item 8 of Part II, “Financial Statements and Supplementary Data—Note 1— Description of Business and Accounting Policies.” 

Critical Accounting Judgments 

The preparation of financial statements in conformity with generally accepted accounting principles of the United States (“GAAP”) requires estimates and assumptions that affect the reported amounts of assets and liabilities, revenues and expenses, and related disclosures of contingent assets and liabilities in the consolidated financial statements and accompanying notes. The SEC has defined a company’s critical accounting policies as the ones that are most important to the portrayal of the company’s financial condition and results of operations, and which require the company to make its most difficult and subjective judgments, often as a result of the need to make estimates of matters that are inherently uncertain. Based on this definition, we have identified the critical accounting policies and judgments addressed below. We also have other key accounting policies, which involve the use of estimates, judgments, and assumptions that are significant to understanding our results. For additional information, see Item 8 of Part II, “Financial Statements and Supplementary Data—Note 1—Description of Business and Accounting Policies.” Although we believe that our estimates, assumptions, and judgments are reasonable, they are based upon information presently available. Actual results may differ significantly from these estimates under different assumptions, judgments, or conditions. 

Inventories 

Inventories, consisting of products available for sale, are primarily accounted for using the first-in first-out (“FIFO”) method, and are valued at the lower of cost or market value. This valuation requires us to make judgments, based on currently-available information, about the likely method of disposition, such as through sales to individual customers, returns to product vendors, or liquidations, and expected recoverable values of each disposition category. These assumptions about future disposition of inventory are inherently uncertain and changes in our estimates and assumptions may cause us to realize material write-downs in the future. As a measure of sensitivity, for every 1% of additional inventory valuation allowance as of December 31, 2015 , we would have recorded an additional cost of sales of approximately $115 million. 

In addition, we enter into supplier commitments for certain electronic device components. These commitments are based on forecasted customer demand. If we reduce these commitments, we may incur additional costs. 

Goodwill 

We evaluate goodwill for impairment annually or more frequently when an event occurs or circumstances change that indicate the carrying value may not be recoverable. During the second quarter of 2015, we changed the measurement date of our annual goodwill impairment test from October 1 to April 1. In testing for goodwill impairment, we may elect to utilize a qualitative assessment to evaluate whether it is more likely than not that the fair value of a