Annuity deposits before coinsurance ceded increased 7% during 2013 compared to 2012 and decreased 22% during 2012 compared to 2011. We attribute the continuing significant sales of our products to several factors including the highly competitive rates on our products, our continued strong relationships with our national marketing organizations and field force of licensed independent insurance agents, the increased attractiveness of safe money products in volatile markets, lower interest rates on competing products such as bank certificates of deposit and product enhancements including a new generation of guaranteed income lifetime withdrawal benefit riders. We attribute the decrease in annuity deposits in 2012 compared to 2011 to certain competitors who were more aggressive in their product pricing. In addition, sales for 2011 benefited from higher demand in advance of rate decreases implemented during that period. The extent to which our high level of sales will be sustained in future periods is uncertain.
Net income, in general, has been positively impacted by the growth in the volume of business in force and the investment spread earned on this business. The average amount of annuity liabilities outstanding (net of annuity liabilities ceded under coinsurance agreements) increased 14% to $29.5 billion for the year ended December 31, 2013 compared to $26.0 billion in 2012 and 16% for the year ended December 31, 2012 compared to $22.4 billion in 2011. Our investment spread measured in dollars was $695.6 million, $596.7 million, and $585.9 million for the years ended December 31, 2013, 2012 and 2011. As previously mentioned, our investment spread in 2013 and 2012 has been negatively impacted by both the extended low interest rate environment and our excess liquidity due to calls of our United States government agency securities (see Net investment income). In addition, net income for the year ended December 31, 2013 was positively impacted by a decrease in the change in fair value of index annuity embedded derivatives due to an increase in the discount rates used to estimate our embedded derivative liabilities (see Change in fair value of embedded derivatives).
Amortization of deferred policy acquisition costs increased 122% to $365.5 million in 2013 and 15% to $164.9 million in 2012 from $143.5 million in 2011. In general, amortization of deferred policy acquisition costs 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, in 2013 and 2012, 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.
Statutory accounting practices prescribed or permitted for our life subsidiaries differ in many respects from those governing the preparation of financial statements under GAAP. Accordingly, statutory operating results and statutory capital and surplus may differ substantially from amounts reported in the GAAP basis financial statements for comparable items. Information as to statutory capital and surplus and statutory net income for our life subsidiaries as of December 31, 2013 and 2012 and for the years ended December 31, 2013, 2012 and 2011 is included in Note 12 to our audited consolidated financial statements.
On July 17, 2013, we issued $400 million aggregate principal amount of senior unsecured notes due 2021 which bear interest at 6.625% per year and will mature on July 15, 2021. We used $15 million of the net proceeds from the issuance to repay the entire amount outstanding under our revolving credit facility and $169 million of the net of proceeds to pay a portion of the cash consideration component of the convertible note exchange offers discussed in Note 9 to our audited consolidated financial statements. We intend to use the $206 million of remaining net proceeds from the notes issuance to tender for, redeem or repurchase the $160 million aggregate principal amount of convertible notes that were outstanding at December 31, 2013. The form and timing of any such activity will be dependent upon market conditions and other factors and there can be no assurance that any such transactions will be completed prior to the December 2014 call date for our 2029 notes or the September 2015 maturity date for our 2015 notes.