60% of Twitter users are leaving 30 days after signing up, claims a Nielsen Online report. Twitter users leave at a rate substantially worse than Facebook and Myspace during its growth period, claims Nielsen.

But is the report accurate?

The report looks at retention rates – how many people stay with Twitter 30 days after signing up – compared to Myspace and Facebook during their growth periods. And the numbers are horrible.

Neilsen claims that 70% of persons stayed with Myspace and Facebook 30 days after joining during the companies’ growth periods, but that at Twitter that number was only 30% recently and now is still at only 40%.

But some question how the statistics may be derived. Ian Paul of PC World finds uncertainty:

While these numbers may sound troubling for Twitter’s future, I think Nielsen could be way off base with this report. …. The reason is that unlike other social networks, Twitter’s primary use is not really as a Website but an Internet-based communications service. That may sound like Web 2.0 nonsense, but consider that once you’ve signed up for Twitter on its Website you could, theoretically, never visit Twitter via a Web browser again. That’s a gigantic difference when you compare Twitter to Facebook and MySpace. … So before we start writing Twitter off as a fad, Nielsen needs to explain how it compiled its data and whether it considered Twitter’s open API in its research.