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  1. #1

    How is market price computed?

    I look at http://theunderminejournal.com/item....eak&item=60838

    the cheapest are 100 singles at 8.88g. I was expecting the "market price" to be 8.88 not the 12.16g. ( Not only does TUJ show the 8.88 but they are the first 2 of the 5 pages in the AH. So I don't know what market price is. Mean? Median?

    1486 7 Available
    12g 16s 2432g 0s Market Price
    -2g 32s -464g 0s Change since Yesterday
    -16.02% Change since Yesterday
    9g 52s 36c 1904g 72s Mean
    2g 42s 73c 485g 46s Standard Deviation

    95% Confidence Interval
    15g 10s 98c 3021g 95s 63c US Alliance Market Price
    14g 40s 56c 2881g 12s US Alliance Mean
    2s 4g 0s Sell to Vendor
    1s 60s 12-hour Deposit
    1s 1g 20s 24-hour Deposit
    1s 20c 2g 40s 48-hour Deposit

  2. #2
    It's a truncated mean with a 15% threshold cut off. It was mentioned in the dev blog some time ago, but cannot find the link. Erorus surely can give you more detail on that.

  3. #3
    Erorus's Avatar
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    Put simply, the market price is the "price per item to buy the cheapest 15% of the quantity available."

    Sort all auctions by order of price per item ascending.
    "N" = Sum quantity available for purchase at any price
    Work your way down the list of auctions, adding the buyouts into the price variable "P", and the quantities into variable "Q", until Q >= 0.15 * N
    Market Price = P/Q
    Last edited by Erorus; April 19th, 2011 at 09:25 PM.

  4. #4
    Thanks!

    Makes sense. You can't let never-going-to-sell high prices inflate it but then you don't want to let a single low-ball change the price.

    P.S. just a curious mathematician:

    Is it 15th percentile or by auction?
    E.G.:
    14 @ 1
    56 @ 5
    30 @ 6
    100 items, mean is 4.74

    So would the market price be 1.27 (19/15) since the bottom 15 cost 19 (14*1+1*5)?
    Or the way I read your algorithm, it would be (14+280)/70 or 4.2

  5. #5
    Erorus's Avatar
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    Quote Originally Posted by hag View Post
    Is it 15th percentile or by auction?
    E.G.:
    14 @ 1
    56 @ 5
    30 @ 6
    100 items, mean is 4.74
    I assume you mean 3 auctions:

    Auction 1 - Quantity: 14, Price: 14g (1g each)
    Auction 2 - Quantity: 56, Price: 280g (5g each)
    Auction 3 - Quantity: 30, Price: 180g (6g each)

    In which case it would be (14+280)/(14+56) = 4.2g

    It's this way because technically you can't buy exactly 15. If you want 15, you're gonna buy the first two auctions, which puts you over (and you'd probably resell the excess). It might look a little off, but this particular example rarely happens in WoW. Either you have commodities, which almost all have a max stack size of 20 and there are many on the AH at once, or you have items you buy in singles, like armor, recipes, pets.. and they typically have a max stack size of 1 and don't have as many up for auction at once.
    Last edited by Erorus; April 19th, 2011 at 10:28 PM.

 

 

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