Headquartered in Louisville, Kentucky, Humana Inc. is one of the nation’s largest publicly traded health benefits companies, based on our 2005 revenues of $14.4 billion. We offer coordinated health insurance coverage and related services through a variety of traditional and Internet-based plans for employer groups, government-sponsored programs, and individuals. As of December 31, 2005, we had approximately 7.1 million members in our medical insurance programs, as well as approximately 1.9 million members in our specialty products programs.
On February 16, 2005, we acquired CarePlus Health Plans of Florida, or CarePlus, as well as its affiliated 10 medical centers and pharmacy company for approximately $444.9 million in cash, including transaction costs, adding approximately 50,400 Medicare Advantage members in Miami-Dade, Broward and Palm Beach counties. This acquisition enhances our Medicare market position in South Florida.
For the Commercial segment, administrative services fees increased $43.4 million, or 26.1%, from $166.0 million for 2004 to $209.4 million for 2005. This increase resulted from increased membership and higher average per member fees. ASO membership of 1,171,000 members at December 31, 2005 increased 15.0% compared to 1,018,600 at December 31, 2004. Average per member fees increased approximately 8% in 2005.
Government segment premium revenues increased 8.8% to $5.7 billion for 2004, compared to $5.3 billion for 2003. This increase primarily was attributable to our Medicare Advantage operations. Medicare Advantage membership was 377,200 at December 31, 2004, compared to 328,600 at December 31, 2003, an increase of 48,600 members, or 14.8%, including 33,100 members added through the acquisition of Ochsner. Average per member premiums for our Medicare Advantage business increased approximately 10% for 2004, reflecting higher reimbursement from CMS. TRICARE premium revenues decreased 5.4% in 2004 reflecting the transition to the new South Region contract which included a temporary loss of approximately 1 million members for 4 months in 2004.
The Commercial segment SG&A expenses increased $35.5 million, or 3.1% during 2004 primarily due to the Ochsner acquisition. The Commercial segment SG&A expense ratio decreased 50 basis points from 16.9% for 2003 to 16.4% for 2004. The Commercial segment SG&A expense ratio for 2003 included an approximate 10 basis point impact from the Jacksonville, Florida building writedown.
We issued in the public debt capital markets, $300 million aggregate principal amount of 7.25% senior unsecured notes that mature on August 1, 2006 and $300 million aggregate principal amount of 6.30% senior unsecured notes that mature on August 1, 2018. We have entered into interest rate swap agreements to exchange the fixed interest rate under these senior notes for a variable interest rate based on LIBOR, as more fully discussed in Note 9 to the consolidated financial statements included in Item 8.-Financial Statements and Supplementary Data.
Our other current Medicaid contract, which is in Florida, is scheduled to expire on June 30, 2006. Due to Medicaid reform in Florida, we are currently negotiating the terms and rates for the renewal contract. We expect the current contract to be extended until August 31, 2006, and the subsequent renewal contract to be effective for a two-year term beginning September 1, 2006. Due to continual decreases in the reimbursement from the state of Illinois, we exited the Illinois Medicaid market effective July 31, 2005. The Illinois and Florida Medicaid contracts accounted for approximately 1% of our total premiums and ASO fees for the year ended December 31, 2005.
The completion and claims per member per month trend factors are the most significant factors impacting the IBNR estimate. The following table illustrates the sensitivity of these factors and the estimated potential impact on our operating results caused by changes in these factors based on December 31, 2005 data:
Our contracts with federal or state governments are generally multi-year contracts subject to annual renewal provisions with the exception of our Medicare Advantage and PDP contracts with the federal government which renew annually. Except for TRICARE contracts discussed in the following section, our government contracts also establish monthly rates per member but may have additional amounts due to us based on items such as age, working status, or specific health issues of the member. For example, CMS has implemented a risk adjustment model which apportions premiums paid to all health plans according to health severity.
Investment securities, which consist primarily of debt securities, have been categorized as available for sale and, as a result, are stated at fair value. Fair value of publicly traded debt and equity securities are based on quoted market prices. Non-traded debt securities are priced independently by a third party. Fair value of venture capital debt securities that are privately held are estimated using a variety of valuation methodologies where an observable quoted market price does not exist. Such methodologies include reviewing the value ascribed to the most recent financing, comparing the security with securities of publicly traded companies in a similar line of business, and reviewing the underlying financial performance including estimating discounted cash flows. Investment securities available for current operations are classified as current assets. Investment securities available for our professional liability and long-term insurance product funding requirements, as well as restricted statutory deposits and venture capital investments, are classified as long-term assets. Unrealized holding gains and losses, net of applicable deferred taxes, are included as a component of stockholders’ equity and comprehensive income until realized from a sale or impairment.
Medical costs include claim payments, capitation payments, pharmacy costs net of rebates, allocations of certain centralized expenses and various other costs incurred to provide health insurance coverage to members, as well as estimates of future payments to hospitals and others for medical care provided prior to the balance sheet date. Capitation payments represent monthly contractual fees disbursed to primary care physicians and other providers who are responsible for providing medical care to members. Pharmacy costs represent payments for members’ prescription drug benefits, net of rebates from drug manufacturers. Receivables for such pharmacy rebates are included in other current assets in the consolidated balance sheet.
Investment securities classified as long-term assets were as follows at December 31, 2005 and 2004:
We have 52% of our Medicare membership and 97% of our Medicaid membership under risk-sharing arrangements with providers. Accordingly, the impact of changes in estimates for prior year medical claims payable on our results from operations that are attributable to our Medicare and Medicaid lines of business may also be significantly reduced, whether positive or negative.
The volatility used to value employee stock options is based on historical volatility. We calculate historical volatility using a simple average calculation methodology based on daily price intervals as measured over the expected term of the option. We have consistently applied this methodology since our adoption of the disclosure provisions of SFAS 123. The decrease in the historical volatility used to value our employee stock options is due to changes in the stock price pattern over the past several years. Our stock price was more volatile in 1998 and 1999 than in recent years. As noted above, we measure volatility over a period equal to the expected term. The average expected term was 6.0 years in 2004, and therefore the period over which volatility was measured when valuing the 2004 stock options included these more volatile years. The combination of the passage of time and the reduction of the expected term to 5.0 years therefore reduced the volatility used to value stock options granted in 2005.
During 2005, we acquired 68,296 of our common shares in connection with employee stock plans at an aggregate cost of $2.4 million, or an average of $34.62 per share.
We also are involved in other lawsuits that arise in the ordinary course of our business operations, including claims of medical malpractice, bad faith, nonacceptance or termination of providers, improper rate setting, failure to disclose network discounts and various other provider arrangements, as well as challenges to subrogation practices. We also are subject to claims relating to performance of contractual obligations to providers, members, and others, including failure to properly pay claims and challenges to the use of certain software products in processing claims. Pending state and federal legislative activity may increase our exposure for any of these types of claims.