RPM get down when I moved from Blogger to wordpress

Hi BHW,
My question is for expert with adsense
mY RPM was about 8-6$ when i used blogger,,but when I moved to wordpress, it got down to 2-3$
Where is the problem ? Has the theme an effect ?
Thanks

I have traffic from USA AUS CAN UK
and RPM still 3-4 $
HELP PLEASE