Matt answered the question in a video for all of us to see, which I have included below, but I have also summarized the main points.

• The information in the Google PageRank toolbar is only updated 3-4 times a year


• This is due to Google now wanting webmasters to become obsessed with PageRank


• Matt advises that webmasters should concentrate their efforts on optimizing their website instead of obsessing about PageRank

In regards to identifying the causes of a PageRank drop, Matt says the main reasons for a PageRank drop are:

• Recent canonicalization changes/ issues


• A drop in the number/quality of websites that link to your site


• The most common reason is because you are selling links from your site. This is a violation of Googles quality guidelines and Google will demote your PageRank to stop those links coming from your site. To reverse this you must remove the links you were selling and submit a reconsideration request to Google.

Check out Matts video answer for more details: