profit or loss that is not meaningful in evaluating the current or future operating performance. Finally, we exclude acquisition costs from AFFO and adjusted EBITDA to allow more comparable comparisons of our financial results to our historical operations. The acquisition costs relate to costs we incur in connection with business combinations. Such charges generally are not relevant to assessing the long-term performance of the company. In addition, the frequency and amount of such charges vary significantly based on the size and timing of the acquisitions. Management believes items such as restructuring charges, impairment charges, gain or loss on asset sales and acquisition costs are non-core transactions; however, these types of costs may occur in future periods.
We define adjusted EBITDA as income or loss from operations excluding depreciation, amortization, accretion, stock-based compensation expense, restructuring charges, impairment charges, acquisition costs, and gain on asset sales as presented below (in thousands):
Three Months Ended
Nine Months Ended
Income from operations
Depreciation, amortization, and accretion expense
Stock-based compensation expense
Gain on asset sales
Our adjusted EBITDA results have improved each year and in each region in total dollars due to the improved operating results discussed earlier in "Results of Operations", as well as the nature of our business model consisting of a recurring revenue stream and a cost structure which has a large base that is fixed in nature also discussed earlier in "Overview".
Funds from Operations ("FFO") and AFFO
We use FFO and AFFO, which are non-GAAP financial measures commonly used in the REIT industry. FFO is calculated in accordance with the standards established by the National Association of Real Estate Investment Trusts. FFO represents net income (loss), excluding gain (loss) from the disposition of real estate assets, depreciation and amortization on real estate assets and adjustments for unconsolidated joint ventures’ and non-controlling interests’ share of these items.
In presenting AFFO, we exclude certain items that we believe are not good indicators of our current or future operating performance. AFFO represents FFO excluding depreciation and amortization expense on non-real estate assets, accretion, stock-based compensation, restructuring charges, impairment charges, acquisition costs, an installation revenue adjustment, a straight-line rent expense adjustment, a contract cost adjustment, amortization of deferred financing costs and debt discounts and premiums, gain (loss) on debt extinguishment, an income tax expense adjustment, recurring capital expenditures and adjustments for unconsolidated joint ventures' and noncontrolling interests’ share of these items and net income (loss) from discontinued operations, net of tax. The adjustments for installation revenue, straight-line rent expense and contract costs are intended to isolate the cash activity included within the straight-lined or amortized results in the condensed consolidated statement of operations. We exclude the amortization of deferred financing costs and debt discounts and premiums as these expenses relate to the initial costs incurred in connection with debt financings that have no current or future cash obligations. We exclude gain (loss) on debt extinguishment since it generally represents the write-off of initial costs incurred in connection with debt financings or a cost that is incurred to reduce future interest costs and is not a good indicator of our current or future operating performance. We include an income tax expense adjustment, which represents the non-cash tax impact due to changes in valuation allowances, uncertain tax positions and deferred taxes that do not relate to current period’s operations. We deduct recurring capital expenditures, which represent expenditures to extend the useful life of its IBX data centers or other assets that are required to support current revenues. We also exclude net income (loss) from discontinued operations, net of tax, which represents results that may not recur and are not a good indicator of our current future operating performance.