Sudden MozRank drop?

[mlwilmore]

My site's MozRank dropped abruptly from 3.5 to 3 from September to October.  MozRank had been steadily climbing until then and there were no changes made to the site in that time period.  What may have happened?

[AdamThompson]

It could just be due to fluctuations in the size of the SEOmoz index and which of your links they indexed this month.