How Much Am I Paid for a Picture Download from Microstock?
http://microstock.pixelsaway.com/how-much-am-i-paid-for-a-picture-download-from-microstock/

I plotted $/download trends for my top 6 sites.

Are you getting similar values from your portfolio?

nice study, are you including PP sales?

It looks eerily close to my numbers....without me actually doing the formal calculations.  The relativeness of your graph is what I feel my RPD is.

I included all type of licenses and PP.

SS going slowly up (the highest RPD was in May 12 with 67 cents, it will continue once I turned 38 cents a few days ago, all time rpd 0.49$)
IS down (PP sales are close to 50% the regular income, all time rpd 0.59$ (1494 regular downloads, 3669 pp downloads)
FT stable (pretty much the same during the last 15 months, turned silver in Jan 12, all time rpd 0.72$)
123RF stable (jumping from 60 cents to 90 cents since the start, all time rpd 0.77$)
DT stable (but higher in the latest 3 months, the only agency that had many times over 1$ RPD, all time rpd 0.84$)