other interest rate swap periodic costs, TBA dollar roll income and dividends on REIT equity securities (referred to as "adjusted net interest and dollar roll income") less (ii) total operating expenses (GAAP measure) adjusted to exclude non-recurring transaction costs (referred to as "adjusted operating expenses"). "Net spread and dollar roll income, excluding 'catch-up' premium amortization," further excludes retrospective "catch-up" adjustments to premium amortization cost or benefit due to changes in projected CPR estimates.
By providing such measures, in addition to the related GAAP measures, we believe we give greater transparency into the information used by our management in its financial and operational decision-making. We also believe it is important for users of our financial information to consider information related to our current financial performance without the effects of certain measures that are not necessarily indicative of our current investment portfolio performance and operations.
Specifically, in the case of "adjusted net interest and dollar roll income," we believe the inclusion of TBA dollar roll income is meaningful as TBAs, which are accounted for under GAAP as derivative instruments with gains and losses recognized in other gain (loss) in our statement of operations, are economically equivalent to holding and financing generic agency MBS using short-term repurchase agreements. Similarly, we believe that the inclusion of periodic interest rate swap settlements in such measure and in "adjusted net interest expense," which are recognized under GAAP in other gain (loss), is meaningful as interest rate swaps are the primary instrument we use to economically hedge against fluctuations in our borrowing costs and inclusion of all periodic interest rate swap settlement costs is more indicative of our total cost of funds than interest expense alone. In the case of "net spread and dollar roll income, excluding 'catch-up' premium amortization," we believe the exclusion of "catch-up" adjustments to premium amortization cost or benefit is meaningful as it excludes the cumulative effect from prior reporting periods due to current changes in future prepayment expectations and, therefore, exclusion of such cost or benefit is more indicative of the current earnings potential of our investment portfolio. We also believe the exclusion of non-recurring transactions costs reported in general, administrative and other expense under GAAP is meaningful as they represent non-recurring transaction costs associated with our acquisition of ACMM and are not representative of ongoing operating costs. In the case of estimated taxable income, we believe it is meaningful information as it is directly related to the amount of dividends we are required to distribute in order to maintain our REIT qualification status.
However, because such measures are incomplete measures of our financial performance and involve differences from results computed in accordance with GAAP, they should be considered as supplementary to, and not as a substitute for, results computed in accordance with GAAP. In addition, because not all companies use identical calculations, our presentation of such non-GAAP measures may not be comparable to other similarly-titled measures of other companies. Furthermore, estimated taxable income can include certain information that is subject to potential adjustments up to the time of filing our income tax returns, which occurs after the end of our fiscal year.
Selected Financial Data
The following selected financial data is derived from our interim consolidated financial statements and the notes thereto. The tables below present our condensed consolidated balance sheets as of June 30, 2016 and December 31, 2015 and our condensed consolidated statements of comprehensive income and key statistics for the three and six months ended June 30, 2016 and 2015 (in millions, except per share amounts):
($ in millions, except per share amounts)
Balance Sheet Data
June 30, 2016
December 31, 2015
Investment portfolio, at fair value
Repurchase agreements, Federal Home Loan Bank advances and other debt
Total stockholders' equity
Net asset value per common share as of period end 1