For 2015, approximately 49.3 percent of our property and casualty statutory direct written premiums were written in Texas, California, Iowa, Missouri and New Jersey; approximately 69.3 percent of our life insurance premiums were written in Iowa, Illinois, Minnesota, Wisconsin and Nebraska.
Income before income taxes for our life insurance segment totaled $6.1 million in 2015 compared to $10.4 million in 2014 and $13.2 million in 2013. The decrease in net income before income taxes from 2014 to 2015 was primarily a result of a decrease in net investment income, an increase in losses and loss settlement expenses and an increase in the increase in liability for future policy benefits, all partially offset by an increase in net premiums earned from higher sales of single premium whole life policies ("SPWL") and a decrease in interest on policyholders' accounts due to a decline in the crediting rate paid on continued net withdrawals of annuity products.
The fixed annuity deposits that we collect are not reported as net premiums earned under GAAP. Instead, we invest annuity deposits and record them as a liability for future policy benefits. The revenue that is generated from fixed annuity products consists of policy surrender charges and investment income. The difference between the yield we earn on our investment portfolio and the interest we credit on our fixed annuities is known as the investment spread. The investment spread is a major driver of the profitability for all of our annuity products. As of December 31, 2015, our investment spread on our annuity products was 1.34 percent as compared to 1.02 percent at December 31, 2014.
Our investment portfolio has a small amount of exposure to energy and certain industrials which were most adversely impacted by the fall in commodity prices. However, the vast majority of those holdings are in highly rated, highly capitalized companies. If this weak commodity environment persists, the credit rating of some of our fixed maturity securities may be downgraded from investment grade to non-investment grade. However, we believe we have ample capacity in the portfolio to manage that transition should it occur. In general, we expect investment yields will remain bounded by central bank monetary policy and the slow pace of global economic growth, and we anticipate periodic spikes in volatility to result in inconsistent liquidity over the near term.
In 2014, our investment income, net of investment expenses, decreased $8.2 million to $104.6 million as compared to 2013, primarily due to a decrease in value of investments that are accounted for under the equity method of accounting and from declining investment yields.
Policy reserves are developed and recorded for deferred annuities, which is an interest-sensitive product, and income annuities. The fair value of the reserve liability for these annuity products is based upon an estimate of the discounted pretax cash flows that are forecast for the underlying business, which is a Level 3 fair value measurement. We base the discount rate on the current U.S. Treasury spot yield curve, which is then risk-adjusted for nonperformance risk and, for interest-sensitive business, market risk factors. The risk-adjusted discount rate is developed using interest rates that are available in the market and representative of the risks applicable to the underlying business.
State insurance holding company laws and regulations generally require approval from the insurer's domicile state insurance Commissioner for any material transaction or extraordinary dividend. For property and casualty insurers, a material transaction is defined as any sale, loan, exchange, transfer or guarantee with an affiliate where the aggregate value of the transaction exceeds 25 percent of the insurer's policyholders' surplus or three percent of its admitted assets (measured at December 31 of the preceding year), whichever is less. For life insurers, a material transaction with an affiliate is defined as a transaction with an aggregate value exceeding three percent of the life insurer's admitted assets (measured at December 31 of the preceding year).
The significant components of our net deferred tax liability at December 31, 2015 and 2014 are as follows: