Annuity product charges (surrender charges assessed against policy withdrawals and fees deducted from policyholder account balances for lifetime income benefit riders) increased 14% to $136.2 million in 2015 and 15% to $119.0 million in 2014 from $103.6 million in 2013. The components of annuity product charges are set forth in the table that follows:
Amortization of deferred policy acquisition costs, in general, has been increasing each year due to the growth in our annuity business and the deferral of policy acquisition costs incurred with respect to sales of annuity products. The increase in amortization from these factors has been affected by amortization associated with fair value accounting for derivatives and embedded derivatives utilized in our fixed index annuity business, amortization associated with net realized gains (losses) on investments and net OTTI losses recognized in operations and the amortization associated with litigation reserves. As discussed above, fair value accounting for derivatives and embedded derivatives utilized in our fixed index annuity business creates differences in the recognition of revenues and expenses from derivative instruments including the embedded derivative liabilities in our fixed index annuity contracts.
The use of this process by the SVO may result in certain non-agency residential and commercial mortgage backed securities being assigned a NAIC designation that is higher than the equivalent NRSRO rating. The NAIC designations for non-agency residential and commercial mortgage backed securities are based on security level expected losses as modeled by an independent third party (engaged by the NAIC) and the statutory carrying value of the security, including any purchase discounts or impairment charges previously recognized. Evaluation of non-agency residential and commercial mortgage backed securities held by insurers using the revised NAIC rating methodologies is performed on an annual basis.
In addition, for debt securities which we do not intend to sell and it is not more likely than not we will be required to sell, but our intent changes due to changes or events that could not have been reasonably anticipated, an other than temporary impairment charge is recognized in net income and amortized cost is written down to fair value. Once an impairment charge has been recorded, we then continue to review the other than temporarily impaired securities for appropriate valuation on an ongoing basis. Unrealized losses may be recognized in future periods through a charge to earnings, should we later conclude that the decline in fair value below amortized cost is other than temporary pursuant to our accounting policy described above. The use of different methodologies and assumptions to determine the fair value of investments and the timing and amount of impairments may have a material effect on the amounts presented in our audited consolidated financial statements.
The liability for lifetime income benefit riders is based on estimates of the value of benefit payments expected to be paid in excess of projected policy values recognizing the excess over the expected lives of the underlying policies. The inputs used in the calculation of the liability for lifetime income benefit riders include actual policy values, actual income account values, actual payout factors, actual roll-up rates and our best estimate assumptions for future policy growth, future policy decrements, the ages at which policyholders are expected to elect to begin to receive lifetime income benefit payments, the percentage of policyholders who elect to receive lifetime income benefit payments and the type of income benefit payments selected upon election. The assumptions are reviewed quarterly and revisions to the assumptions are made based on historical results and our best estimates of future experience. The liability for lifetime income benefit riders is included in policy benefit reserves in the consolidated balance sheets and the change in the liability is included in interest sensitive and index product benefits in the consolidated statements of operations. See Results of Operations for the Three Years Ended December 31, 2015 in this Item 7. for a discussion and presentation of the actual effects of assumption revisions.