That's what I'm on about as this 1 in 3 means little if the average time on the pitch is low.
If Defoe averages just 50 mins on the pitch for us would you still expect him to get 1 goal in 3 appearances? He only averaged 63 mins with Spurs which isn't low but certainly isn't high but here's hoping he gets into the high 70's for us as he will be the main man.
Look at Lampard's stats this season for example, 5 goals in 16 appearances which itself is canny as it's just under 1 in 3 (3.2 apps/goal to be exact). Seeing as he's only been on the pitch a total of 371 mins (average 23 mins per appearance) then he's getting a goal every 74 mins he's on the pitch.
Now compare that to Toure who has 7 goals in 18 appearances which is 2.57 appearances per goal and better than Lampard's 3.2. Therefore most will say Toure has the better goal stat but he hasn't by a long way! Toure has played a total of 1523 mins so averages 84 mins per appearance. He gets a goal every 217 minutes he's on the pitch compared to the 74 mins it takes Lampard to get a goal.
This is the 1st example I picked but I'm sure there are more. That's why appearances per goal isn't a good stat IMO, it's just easier to work out for most people as the info is easily found. As there are more detailed stats available then why not break it down a bit more and get a truer reflection of a player's goal return?