dependent or not??

The alexa of my site has dropped from 847,879 to 657,987 but there is increase in the traffic. However the case is different with my other site which is having the good alexa but low traffic.

I want to know that Is alexa dependent on traffic to a site??

Alexa is independent of the traffic on your site. it has nothing to do with the traffic coming on your site. It depends on the the fact that if the visitor of your site have alexa toolbar installed.