When it comes to bond funds — or any mutual funds — past performance is not the best way to analyze them. Instead, S&P Capital IQ analyst Todd Rosenbluth suggests investors should consider the credit risk of the underlying bonds, as well as a fund’s duration (price sensitivity to changes in interest rates).

Expense ratios and the length of a fund manager’s tenure are other key considerations.

With all that in mind, Rosenbluth identified two taxable fixed-income funds with over $50 million in assets that have fairly low S&P Capital IQ ratings, despite the fact that they’ve performed well over the past several years.

The funds are: Calvert Long Term Income Fund (CLDAX) and PIMCO Emerging Markets Bond Fund (PAEMX). Calvert, a corporate debt fund, gets a two-star ranking out of a possible five stars from S&P Capital IQ, based on what the research group says is high duration relative to its peers. Also, 8% of the fund’s bonds were rated BB or below as of last September. Finally, the recent managers of the fund have all been relatively new to leading it, even if they are not new to the firm, and the expense ratio at 1.25% is higher than its peer group average, according to the report.

As for the PIMCO emerging markets fund, which gets three stars, it also has above-average duration compared to other taxable fixed-income funds and has a large holding of bonds with higher credit risk, according to the report. Approximately 50% of the bonds were BBB and 20% were BB or lower, as of last September. The fund’s manager has also had a relatively short tenure, having taken over just a year ago, though he has been at PIMCO for more than five years. Still, “we caution investors from relying solely on the fund’s above-average three-year track record versus its emerging market peers,” Rosenbluth said in the report.

Danielle Reed writes for Financial Planning.