According to Ryan Labs, pension fund asset growth was 26 percent behind liability growth through Dec. 13, 2000. This negative asset-to-liability ratio erases the 26 percent increase in asset growth over liability growth that occurred in 1999. The report issued by Ryan Labs cites falling interest rates and poor investments as the leading causes of the assets vs. liabilities gap. Because pension surpluses can add to a company's bottom line, increases in pension fund liabilities become a drain on the bottom line. According to Sean McShea of Ryan Labs, companies can invest pension funds in bonds, which protect the pension fund from drops in the Standard & Poor's 500 stock index, but also only allow the fund to gain half of the revenue from increases in the index. McShea recommends that companies take into account long-term liabilities and determine how much of an asset surplus is needed to cover future liabilities before making portfolio changes. For example, Kentucky Retirement Systems conducts a study every five years to project future liabilities and to determine how the fund's money can best be invested.