Hi Jane,

 Compete toolbar data is much more accurate than alexa data. You can learn about how compete and alexa differ in our blog at http://blog.compete.com/2006/12/11/compete-vs-alexa-competitive-site-metrics/

 tzvika - Based on the daily web usage of more than two million people, Compete calculates and estimates total traffic and rank for nearly every site on the web. We balance multiple data sources, including ISPs, ASPs, Opt-In Panels and the Compete Toolbar. We strongly believe in our multiple data source strategy and its ability to detect and correct for bias across diverse data sources to ensure accurate U.S. projections.

***Full Disclosure - I work for Compete***