There is a big difference between the repayment rates for ended, and portfolio at risk for currently outstanding loans. In order to have a complete picture, lenders should know the performance of currently outstanding loans as well as ended ones. Zidisha is the only microlending website I know of that provides statistics on the performance of the currently outstanding loan portfolio.
Even our statistics for ended loans are not defined in the same way as other websites. For example, I understand that Kiva expresses its repayment rate as 100% minus the writeoff rate, including as repaid loans amounts not yet repaid, but not yet written off. (http://www.kivafriends.org/index.php?topic=5791.0)
More importantly, I understand that Kiva allows field partners to cover repayments not actually made by the borrowers and report these amounts as paid on the Kiva website. (http://blog.givewell.org/2009/10/13/kiva-repayment-data/) These amounts are repaid in that lenders do receive the funds back, and I am not accusing Kiva of dishonesty. But the fact remains that substantially less than 98.95% of Kiva loans are repaid by the borrowers themselves.
I have lived with many low-income households in developing countries, and in my experience, cash availability of households without formal jobs, insurance, savings or social safety nets is not only limited, but highly irregular. It is simply not realistic to provide people under these circumstances enough capital to change their lives, and expect its repayment to obey a predetermined schedule with 98.9 percent accuracy. That is why I am skeptical of such high published repayment rates.
Zidisha's published rates are lower, but they do accurately reflect the repayment performance of the borrowers themselves. Comparing them with the statistics of intermediated microlending websites is misleading, because they are not measuring the same thing.
I have not managed to find information on how Kiva Zip's repayment rate is defined, so cannot comment on it.