It is most likely digital sales + physical shipment, yes. Thanks for correcting me

I've been thinking of doing this for a while, but it would take quite some time and effort to put into motion.

Without developers saying, we can never trully know exactly how many sales a digital game has, but quite a few online games have online leaderboards. I thought it may be possible, to see how many players have a score on the leaderboard (so the total number of players) and compare that to the digital ratings the games have recieved online (we'd then make a graph which can hopefully let us predict reasonably well how much other games have sold).

There are a few catchs of course, we'd have to exclude games released AT ALL physically, as this would affect the leaderboard numbers and as krafty89 said, if you buy a game once on the PS Store, you can download to another PS3/PSV for free, so that would have an affect too. But it would be better than nothing :P

I think five percent of software downloads are rated has enough evidence to it that we can use it to start extrapolating numbers

Let's crunch some numbers!

To start off the PS Vita has sold half a million in America. Uncharted has sold .18 million in America according to vgchartz. That means 36% of Vita owners bought Uncharted. However, what about digital? At least for me 70% of my PSN friends with a Vita have Uncharted. So using these numbers we can say Uncharted has roughly a 1 to 1 ratio of physical to digital. So we can say it has been downloaded about 170 thousand times. Sadly people who download the free demo can rate it but it has right over 4,000. This meansonly about 2 percent have rated the game who bought it. So for every other big game I think 10 percent is a good lowball.

Interesting. Tagged!

Awesome thanks. I'll update it now (will take a while)

Oh dear god...

If this 1 to 1 ratio were remotelly near the truth, Sony would have bragged about it.

Unity 13, Rayman and Wipeout, for example, have demos on US PSN. After downloading the demo you can rate as it you bought the game (I myself did it). Sadly this affects the idea of this topic :( 

Posting on the PS3 so I cant use any format so without further ado ratings from the HK psn store

note: J (Japanese version)
E (English version )
C ( Chinses version )

Army Corps of Hell : 12 (E) 45 (J)
BlazBlue: Continuum Shift Extend : 121
Disgaea 3: Absence of Detention : 59 (E) 83 (J)
Dynasty Warriors Next : 190 (J) 117 (C) 80 (E)
Escape Plan : 749
Everybody's Golf 6 : 263 (E/C) 169 (J)
F1 2011 : 12
Hustle Kings : 265
Lego Harry Potter: Years 5–7 : 12
Gravity Rush : 2008 (C)
Little Deviants : 611
Lord of Apocalypse : 144 (J)
Lumines Electronic Symphony : 71
Surge Concerto: Ciel Nosurge : 63
MLB 12: The Show : 24
Michael Jackson: The Experience : 26 (E) 7 (J)
ModNation Racers: Road Trip 32
Mortal Kombat : 24
MotorStorm: RC : 215
Ninja Gaiden Sigma Plus : 220 (J/E) 208 (J/E)
Touch My Katamari : 53 (J)
Dream Club Zero Portable : 29 (C)
FIFA 12 : 138 (E)
Ragnarok Odyssey : 1285 (J)
Rayman Origins : 117 (E)
Reality Fighters: 55 (E)
Shinobido 2: Tales of the Ninja : 54 (E/C) 61 (J)
Super Stardust Delta : 204 (J) 206 (E)
StarDrone Extreme : 91 (E)
Sumioni: Demon Arts : 55
Virtua Tennis 4: World Tour Edition : 201
Wipeout 2048 : 218
Tales from Space: Mutant Blobs Attack : 1215 (E)
Tales of Innocence R : 266 (J)
Ultimate Marvel vs. Capcom 3 : 107 (J) 34 (E)
Uncharted: Golden Abyss : 534
Unit13 : 211