15. SEGMENT, MAJOR CUSTOMER AND MAJOR SUPPLIER INFORMATION Segment Information Due in part to the regional nature of supply and demand of aluminum rolled products and in order to best serve our customers, we manage our activities on the basis of geographical areas and are organized under four operating segments: North America, Europe, Asia and South America. We measure the profitability and financial performance of our operating segments based on Segment income. Segment income provides a measure of our underlying segment results that is in line with our portfolio approach to risk management. We define  Segment income  as earnings before (a)  depreciation and amortization ; (b)  interest expense and amortization of debt issuance costs ; (c)  interest income ; (d)  unrealized gains (losses) on change in fair value of derivative instruments, net , except for foreign currency derivatives on our foreign currency balance sheet exposures, which are included in segment income; (e)  impairment of goodwill ; (f) impairment charges on long-lived assets (other than goodwill); (g) gain or loss on extinguishment of debt; (h) noncontrolling interests  share; (i) adjustments to reconcile our proportional share of  Segment income  from non-consolidated affiliates to income as determined on the equity method of accounting; (j)  restructuring charges, net ; (k) gains or losses on disposals of property, plant and equipment and businesses, net; (l) other costs, net; (m) litigation settlement, net of insurance recoveries; (n) sale transaction fees; (o) provision or benefit for taxes on income (loss) and (p) cumulative effect of accounting change, net of tax. Adjustment to Eliminate Proportional Consolidation. The financial information for our segments includes the results of our non-consolidated affiliates on a proportionately consolidated basis, which is consistent with the way we manage our business segments. However, under US GAAP, these non-consolidated affiliates are accounted for using the equity method of accounting. Therefore,