When using a pricing service, we obtain the vendor's pricing methodology documentation to ensure we understand their methodologies. We periodically review and approve the selection of the pricing vendors we use to ensure we are in agreement with their methodologies. We also review the reasonableness of sources and inputs used in developing pricing. When markets are less active, brokers may rely more on models with inputs based on the information available only to the broker. We monitor securities priced by brokers and evaluate their prices for reasonableness based on benchmarking to available primary and secondary market information. In weighing a broker quote as an input to fair value, we place less reliance on quotes that do not reflect the result of market transactions. We also consider the nature of the quote, particularly whether the quote is a binding offer. If prices in an inactive market do not reflect current prices for the same or similar assets, adjustments may be necessary to arrive at fair value. When relevant market data is unavailable, which may be the case during periods of market uncertainty, the income approach can, in suitable circumstances, provide a more appropriate fair value. During 2011, we have applied valuation techniques on a consistent basis to similar assets and liabilities and consistent with those techniques used at year end 2010.
Interest and debt expense in 2011 was marginally higher than 2010 due primarily to the September 2010 issuance of $400.0 million of debt, mostly offset by the maturity of $225.1 million of debt in March 2011. We also experienced lower interest expense in 2011 compared to 2010 on $350.0 million of debt which we effectively converted into floating rate debt through the use of an interest rate swap entered into during the fourth quarter of 2010. Interest and debt expense for 2010 was higher than in 2009 due to higher levels of outstanding debt, partially offset by lower rates of interest on our floating rate debt issued by Northwind Holdings and Tailwind Holdings. See "Debt" contained in this Item 7 for additional information.
Year Ended December 31, 2010 Compared with Year Ended December 31, 2009
Sales of voluntary benefits increased 15.6 percent in 2010 relative to 2009, and the number of new accounts increased 13.3 percent. Sales in our individual disability - recently issued line of business decreased 17.2 percent in 2010 compared to 2009.
In the current competitive pricing market and economic environment, we continue to have a cautious outlook for premium growth. We anticipate returning to more normalized levels of premium growth through stable persistency and price increases, as well as increased sales to existing and new customers which we expect to occur commensurate with the timing of the U.K. economic recovery. We expect our overall benefit ratio in 2012 to be favorable compared to 2011. We expect our profit margins to continue at a favorable level, consistent with 2011.
The duration weighted book yield on the fixed income securities in our investment portfolio was 6.67 percent as of December 31, 2011, compared to a yield of 6.71 percent as of December 31, 2010. As previously noted, we actively manage our asset and liability cash flow match and our asset and liability duration match to limit interest rate risk. Duration is a measure of the percentage change in the fair values of assets and liabilities for a given change in interest rates. Cash flows from the in-force asset and liability portfolios are projected at current interest rate levels and also at levels reflecting an increase and a decrease in interest rates to obtain a range of projected cash flows under the different interest rate scenarios. These results enable us to assess the impact of projected changes in cash flows and duration resulting from potential changes in interest rates.
During 2009, we recognized a loss of $14.2 million on the sale of securities issued by a large publisher of yellow page advertising. The company had suffered from deterioration in print directories' advertising as well as a significant rise in bad debt expenses due to the impact of the recession on small business customers. The company maintained significant amounts of available cash and was still generating free cash flows despite the weakening economy. However, during the first quarter of 2009, the company announced that it had hired a financial adviser to review its capital structure alternatives regarding debt payments due in 2010. At the time of disposition, these securities had been in an unrealized loss position for a period of greater than three years.
At December 31, 2011, our mortgage/asset-backed securities had an average life of 4.28 years, effective duration of 3.78 years, and a weighted average credit rating of AAA. The mortgage/asset-backed securities are valued on a monthly basis using valuations supplied by the brokerage firms that are dealers in these securities as well as independent pricing services. One of the risks involved in investing in mortgage/asset-backed securities is the uncertainty of the timing of cash flows from the underlying loans due to prepayment of principal with the possibility of reinvesting the funds in a lower interest rate environment. We use models which incorporate economic variables and possible future interest rate scenarios to predict future prepayment rates. The timing of prepayment cash flows may also cause volatility in our recognition of investment income. We recognize investment income on these securities using a constant effective yield based on projected prepayments of the underlying loans and the estimated economic life of the securities. Actual prepayment experience is reviewed periodically, and effective yields are recalculated when differences arise between prepayments originally projected and the actual prepayments received and currently projected. The effective yield is recalculated on a retrospective basis, and the adjustment is reflected in net investment income.
Net cash provided by operating activities was $1,193.7 million for the year ended December 31, 2011, compared to $1,196.8 million and $1,237.0 million for 2010 and 2009, respectively. Operating cash flows are primarily attributable to the receipt of premium and investment income, offset by payments of claims, commissions, expenses, and income taxes. Premium income growth is dependent not only on new sales, but on renewals of existing business, renewal price increases, and persistency. Investment income growth is dependent on the growth in the underlying assets supporting our insurance reserves and on the earned yield. The level of commissions and operating expenses is attributable to the level of sales and the first year acquisition expenses associated with new business as well as the maintenance of existing business. The level of paid claims is affected partially by the growth and aging of the block of business and also by the general economy, as previously discussed in the operating results by segment. Operating cash flows for 2010 and 2009 include pension contributions of approximately $176.9 million and $79.7 million, respectively.
Purchases of available-for-sale securities were lower in 2011 compared to 2010 as a result of the decline in funds available for reinvestment due to the decrease in bond calls, as discussed above. Purchases of available-for-sale securities were slightly lower during 2010 relative to 2009. Although investable funds were available in 2010 for reinvestment due to the increase in proceeds from bond calls and maturities, as previously noted, the deployment of funds was hampered by the lack of available long-term securities which met our investment objectives.
Net purchases of short-term investments decreased in 2011 compared to 2010 due to our use of cash to fund the payment for our debt maturing in 2011 and to also fund the 2011 repurchases of Unum Group common stock. This decline in net purchases was partially offset by an increase in purchases of short-term investments using cash received under our securities lending program. Net purchases of short-term investments increased during 2010 relative to 2009 due to the increase in bond calls and maturities, with the proceeds invested in short-term investments pending the purchase of fixed maturity securities.
for our employees, including non-qualified pension plans. Pension plan obligations, other than the non-qualified plans, represent our expected contributions to the pension plans. Amounts in the one year or less category equal our expected contributions within the next 12 months. The remaining years' contributions are projected based on the expected future contributions as required under the Employee Retirement Income Security Act (ERISA). Non-qualified pension plan and other postretirement benefit obligations represent the expected benefit payments related to these plans. The pensions and other postretirement benefit projections reflect expected future service. These projections are not discounted with respect to interest and therefore exceed the amount recorded in the consolidated balance sheets. See Note 8 of the "Notes to Consolidated Financial Statements" contained herein in Item 8 and "Critical Accounting Estimates" contained in this Item 7 for additional information.
Miscellaneous liabilities include commissions due and accrued, deferred compensation liabilities, state premium taxes payable, amounts due to reinsurance companies, accounts payable, obligations to return unrestricted cash collateral to our derivatives counterparties, and various other liabilities that represent contractual obligations. Obligations where the timing of the payment was uncertain are included in the one year or less category. See Note 4 of the "Notes to Consolidated Financial Statements" contained herein in Item 8 for additional information on our derivatives.
To manage our cash position more efficiently, we enter into repurchase agreements with unaffiliated financial institutions. We generally use repurchase agreements as a means to finance the purchase of invested assets or for short-term general business purposes until projected cash flows become available from our operations or existing investments. Our repurchase agreements are typically outstanding for less than 30 days. We post collateral through our repurchase agreement transactions whereby the counterparty commits to purchase securities with the agreement to resell them to us at a later, specified date. The fair value of collateral posted is generally 102 percent of the cash received.
In July 2010, the FASB issued an update to require additional disclosures regarding the credit quality of financing receivables, including the entity's credit risk exposure, its assessment of risk in estimating its allowance for credit losses, changes in the allowance for credit losses and the reason for those changes, and troubled debt restructuring. We adopted all of the required disclosures effective December 31, 2010 except for troubled debt restructuring disclosures which were deferred by the FASB. The adoption of this update expanded our disclosures but had no effect on our financial position or results of operation.
In June 2011, the FASB issued an update related to the financial statement presentation of comprehensive income. This update will require that non-owner changes in stockholders' equity be presented either in a single continuous statement of comprehensive income or in two separate but consecutive statements. In the two-statement approach, the first statement should present net income and its components, followed consecutively by a second statement presenting total other comprehensive income, the components of other comprehensive income, and the total of comprehensive income. In December 2011, the FASB issued an update to indefinitely defer the effective date pertaining to the presentation of reclassification adjustments and reinstated the previous requirement to present reclassification adjustments either on the face of the statement or in financial statement footnotes. The amendments in this update are effective for interim and annual periods beginning after December 15, 2011. The adoption of this update will modify our financial statement presentation but will have no effect on our financial position or results of operations.
Mortgage Loans: Fair values are estimated using discounted cash flow analyses and interest rates currently being offered for similar loans to borrowers with similar credit ratings and maturities. Loans with similar characteristics are aggregated for purposes of the calculations.
We are the sole beneficiary of a special purpose entity which is consolidated under the provisions of GAAP. This entity is a securitized asset trust containing a highly rated bond for principal protection, nonredeemable preferred stock, and several partnership equity investments. We contributed the bond and partnership investments into the trust at the time it was established. The trust supports our investment objectives and allows us to maintain our investment in the partnerships while at the same time protecting the principal of the investment. There are no restrictions on the assets held in this trust, and the trust is free to dispose of the assets at any time. Because the assets in the trust are not liquid investments, we periodically provide funding to the underlying partnerships in the trust upon satisfaction of contractual notice from the partnerships. The fair values of the bond, nonredeemable preferred stock, and partnerships were $121.3 million, $0.1 million, and $8.0 million, respectively, as of December 31, 2011. The bonds are reported as fixed maturity securities, and the nonredeemable preferred stock and partnerships are reported as other long-term investments in our consolidated balance sheets. At December 31, 2011, we had non-binding commitments to fund approximately $0.5 million to the underlying partnerships. The amount of funding provided to the partnerships during the years ended December 31, 2011 and 2010 was de minimis.
As of December 31, 2011 and 2010, we had $335.0 million and $540.0 million, respectively, notional amount of forward starting interest rate swaps to hedge the anticipated purchase of fixed maturity securities.
The Unum UK segment includes insurance for group long-term disability, group life, and supplemental and voluntary lines of business. The supplemental and voluntary lines of business are comprised of individual disability, critical illness, and voluntary benefits products. Unum UK's products are sold primarily in the United Kingdom through field sales personnel and independent brokers and consultants.