Tempted by an attractive yield on a bond fund? Better be sure you know which yield you’re looking for.

Some fund sellers quote a type of figure for a fund’s income return that can be a full percentage point or more higher than the standardized yield calculations mandated by the Securities and Exchange Commission.

Consider, for instance, T Rowe Price Tx Fr Inc Tr Intmed Bond (PTIBX). The fund’s recent SEC yield, as listed on the fund firm’s Web site, is 2.39%. But the “annualized dividend” yield listed just above that figure is a more substantial 3.79%.

Similarly, the “distribution rate” for MFS Bond Fund/A (MFBFX) is over 5% while the SEC yield is 3.97%, according to the MFS Web site. Many stockbrokers and other fund sellers focus on the figure they call the dividend yield or the distribution rate rather than the SEC yield, says Jim Swanson, a portfolio manager and fixed-income strategist at MFS Investment Management in Boston.

With interest rates at their lowest levels in decades, many conservative investors are desperate to wring as much income as they can out of their bond portfolios. Officials at fund firms MFS and T. Rowe Price Group say the SEC yield and the distribution rate can provide useful information to bond fund shoppers.

The risk for investors is that some fund sellers may quote only the higher distribution rate without making clear that the figure is not directly comparable to other funds’ SEC yields.

Further, the distribution figure “doesn’t give the full picture” of a bond fund’s income generating potential, says Gene Gohlke, an associate director of the SEC Office of Compliance Inspections and Extensions who helped draft the yield rules in the 1980s.

The SEC yield is an attempt to provide uniformity among funds and also give “a more accurate picture” of funds’ income producing potential to investors, he says. That’s why the SEC since 1988 has required funds to quote the SEC yield whenever they choose to advertise their yields.