Our ability to price our life insurance products to earn acceptable margins over the cost of providing benefits and the expenses of acquiring and administering the products. Competitive conditions, mortality experience, persistency, investment results and our ability to maintain expenses in accordance with pricing assumptions drive our margins on the life products. On many products, we have the ability to mitigate adverse experience through adjustments to credited interest rates, policyholder dividends or cost of insurance charges.
U.S. net farm income is estimated to have decreased 38.2% and farm real estate value is estimated to have decreased 1.6% during 2015 according to the U.S. Department of Agriculture.
Earnings per share from continuing operations benefited from the repurchase of Class A common shares in 2014 and 2013, as well as a tender offer for Class B common shares completed in the third quarter of 2013. Details regarding the share repurchases are included in Note 7 to the consolidated financial statements included in Item 8.
balances. While the unlocking process can take place at any time, as needs dictate, the process typically takes place annually. See the discussion that follows for further details of the unlocking impact to our operating segments.
Pre-tax operating income for the Life Insurance segment increased in 2015 and 2014 compared to prior periods. The increase in 2015 was primarily due to an increase in the volume of business in force, higher investment fee income and the impact of unlocking, partially offset by increases in death benefits and other underwriting expenses. The increase in 2014 was primarily due to an increase in the volume of business in force, partially offset by the impact of the correction of an immaterial error which increased pre-tax earnings by $2.8 million in 2013. This correction was related to a reclassification of certain product loads from deferred revenue to earned income and increased interest sensitive product charges $6.3 million, changes in reserves classified with interest sensitive death benefits $2.5 million and amortization of deferred acquisition costs $1.0 million.
Future policy benefits increased 4.5% to $6,401.5 million at December 31, 2015 primarily due to an increase in the volume of annuity and life insurance business in force. Deferred income taxes decreased 34.3% to $135.1 million at December 31, 2015, primarily due to the tax impact of the change in unrealized appreciation/depreciation on investments. Liabilities related to separate accounts decreased 8.5% to $625.3 million primarily due to the impact of changes in market performance.
A majority of our insurance liabilities are backed by fixed maturity securities and mortgage loans. The weighted average life of the fixed maturity and mortgage loan portfolio, based on fair values, was approximately 10.9 years at December 31, 2015 and 10.6 years at December 31, 2014. Accordingly, the earned rate on the portfolio lags behind changes in market yields. The extent that the portfolio yield lags behind changes in market yields generally depends upon the following factors:
We earn mortality and expense fee income based on the value of our separate accounts at annual rates ranging from 0.00% to 1.45% for 2015, 2014 and 2013. As a result, revenues from these sources fluctuate with changes in the fair value of the equity, fixed maturity and other securities held by the separate accounts.
Policy loans are reported at unpaid principal balance. Short-term investments, which include investments with remaining maturities of one year or less, but greater than three months at the time of acquisition, are reported at cost adjusted for amortization of premiums and accrual of discounts. Other investments include call options, which are carried at fair value, a promissory note acquired in a sale of a partnership interest, which is carried at the remaining basis of the partnership, and our
Deferred acquisition costs include certain costs of successfully acquiring new insurance business, including commissions and other expenses related to the production of new business, to the extent recoverable from future policy revenues and gross profits. Also included are premium bonuses and bonus interest credited to contracts during the first contract year only. The value of insurance in force acquired represents the cost assigned to insurance contracts when an insurance company is acquired. The initial value is determined by an actuarial study using expected future gross profits as a measurement of the net present value of the insurance acquired. Interest accrued on the unamortized balance at a weighted average rate of 4.84% in 2015, 4.84% in 2014 and 4.94% in 2013.
Bureau Life. Participating business accounted for 31% of receipts from policyholders during 2015 (2014 and 2013 - 30%) and represented 11% of life insurance in force at December 31, 2015, 2014 and 2013.
Traditional life insurance premiums are recognized as revenues over the premium-paying period. Future policy benefits and policy acquisition costs are recognized as expenses over the life of the policy by means of the provision for future policy benefits and amortization of deferred acquisition costs.
Comprehensive income includes net income, as well as other comprehensive income items not recognized through net income. Other comprehensive income includes unrealized gains and losses on our available-for-sale securities as well as the underfunded obligation for certain retirement and postretirement benefit plans. These items are included in accumulated other comprehensive income, net of tax and other offsets, in stockholders' equity. The changes in unrealized gains and losses reported in our Statement of Comprehensive Income (Loss), excludes net investment gains and losses included in net income which represent transfers from unrealized to realized gains and losses. These transfers are further discussed in Note 7. The components of the underfunded obligation for certain retirement and postretirement benefit plans are provided in Note 8.
Level 2 other investments include call options with fair values based on counterparty market prices adjusted for a credit component of the counterparty, net of collateral received.
Farm Bureau Life may cede certain losses under an annual 100% quota share accidental death reinsurance agreement. Coverage includes all acts of terrorism including those of a nuclear, chemical or biological origin. Coverage is subject to an annual aggregate retention of $14.1 million. A maximum occurrence limit of $50.0 million per aircraft applies to policies written on agents of the Company who are participating in company-sponsored incentive trips. Additionally, a $200.0 million occurrence limit applies to employees in the home office building, net of reinsurance on group life policies. All other occurrence catastrophes are unlimited in amount.
Short-term debt consists of two short-term advances, collateralized by fixed maturity securities, payable to FHLB totaling $15.0 million at December 31, 2015. The advances include a $10.0 million advance on December 21, 2015, due January 11, 2016, with an interest rate of 0.55% and a $5.0 million advance on December 30, 2015, due January 6, 2016, with an interest rate of 0.46%.
Net periodic pension cost of the Multiemployer Plan is allocated between participating employers on a basis of time incurred by the respective employees for each employer. Such allocations are reviewed annually. This Multiemployer Plan is not subject to collective bargaining agreements, a financial improvement plan or a rehabilitation plan. No surcharges were required to be paid to the Multiemployer Plan during 2015, 2014 or 2013. We are the primary employer in the Multiemployer Plan, providing more than 5 percent of the total contributions during 2015, 2014 and 2013.
We expect contributions to be paid to the Multiemployer Plan by us and affiliates for 2016 to be approximately $15.0 million, of which $4.8 million is expected to be contributed by us. We expect contributions to be paid to the Other Plans by us and affiliates for 2016 to be approximately $2.4 million, of which $1.2 million is expected to be contributed by us. Expected benefits to be paid under the Multiemployer Plan are as follows: 2016 - $17.5 million, 2017 - $15.5 million, 2018 - $17.6 million, 2019 - $17.5 million, 2020 - $19.1 million and 2021 through 2025 - $109.1 million. Expected benefits to be paid under the Other Plans are as follows: 2016 - $3.0 million, 2017 - $1.8 million, 2018 - $2.1 million, 2019 - $2.4 million, 2020 - $2.3 million and 2021 through 2025 - $8.7 million.
Farm Bureau Life has a subsidiary, Greenfields, which launched in 2013 and is regulated by the Colorado Division of Insurance. Greenfields' operations are immaterial and implicitly included in the financial results of Farm Bureau Life below.