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zargblatt

Why does WN8 sum not match individual tank WN8 sum

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So i download my 30 day statistics into excel. It contains a WN8 number per tank and i do some math on my own.

Wotlabs average says 1931,  but if i take average of the WN8 per tank column (without taking into account the number of games) i get 1801.

If i multiply each tank WN8 with number of games, add them together and divided by total games i get 2246.

 

Are there some hidden formula that takes tier, or number of games into account when calculating WN8 across multiple vehicle? Othervise the math seems wrong...

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average tier,  and other stuff would change for the overall and per tank.

Im not sure how the formula works myself, but the way I'd understand it is that if you played one battle in a T5 tank, and one battle in a T10 tank, with both being at say exactly 3000 WN8, when adding them together for the overall stat, your average tier of 7.5 would yield slightly different expected values than a simple case of "this tanks expected plus this tanks expected divided by 2" 

Ok so I just tried this, the M4 Shermans expected (513.45) plus the M48 Pattons expected (1864.403) divided by two is 1188.9265. for an Average tier of 7.5. but the T20s expected is 944.827, and the Pershing is 1119.194. So just by adding the expected damages, your average tier of 7.5 already has higher expected than a tier 8 tanks expected. 

I could be talking completely out of my ass here, but thats how I'd understand it working. This basic premise would also apply to spots, kills, and all the other stats that get included.

 

also its more likely that the per tank is wrong and not the overall, as WN8 is intended to show stats over a large sample size and for smaller sample sizes or even for per tank, its not entirely accurate. 

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According to this article the calculation of WN8 doesnt take into account tier:

http://forum.worldoftanks.eu/index.php?/topic/547149-wn8-formula-detailed-breakdown-stat-nerds-should-drop-by/

I think the creator of WN8 made a matchematical blunder! 

If the calculation of individual tanks are correct then the sum of a group of tanks should be the weighted average. Any discrepancy is mathematically wrong...

 

 

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It works this way because the formula calculates your WN8 over your account-wide stats ((a+b)/(A+B)) and not for each tank (a/A+b/B), and because (a/A+b/B) is not equal to (a+b)/(A+B), there is a discrepancy. It would be too computationally intensive to do it the other way, because there is just too much data to process for that many accounts at a time (on WoTLabs' or XVM's end).

Naturally, since damage is the highest weighted stat in the formula, battles in higher-tiered tanks are going to have a greater influence on that part of the formula and therefore the final result.

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