Author:  Gaston.La.Brick  Posted:  Oct 1, 2018 08:47  Subject:  90-percentile as new average price ?  Viewed:  203 times  Topic:  Suggestions  Status: Discarded Cancel Reply

BrickLink ID Card Gaston.La.Brick (1841) Location:  Belgium Member Since Contact Type Status Nov 12, 2016 Seller  Store: The Rolling Bricks

I noticed the highest prices of items sold (or of items that are on sale), have an out of proportion influence on the average prices. Example: when 9 people sell (or have sold) an item at €0.10 but 1 person has sold that item for €10.00, the average price would be €1.09 You may say this example is not realistic, but it's not that unrealistic either. Check out item 6558. The avg used price of last 6 month sales is €0.023, while the majority of the sales are for less as €0.02 If you look more closesly, you see a few sales at a high price, but not a lot. (Note: someone even sold a few of these for €1.00 !) It's my suggestion to change the calculation of avg price to use the 90-percentile method. So only the 90 percent (lowest prices) are taken into account. That way, the top 10-percent highest prices are not taken into account when calculating the avg price. To avoid weird behaviours, the rule could be in place only when there are 10 items sold/for sale. Example would become an avg price of €0.10 Another somewhat more complex method would be the use the median. Not the mathematic average, but the middle price: 50% of the sellers have a lower price, 50% of the sellers have a higher price. What do you guys think?

Message Has 3 Replies:

Re: 90-percentile as new average price ? - Teup (6606)

[...] This suggestion comes up now and then, I am not in favour, as it makes the priceguide less transparent but most of all it promotes the race to the bottom even more. In [...] (69 months ago, Oct 1, 2018, to Suggestions)

Re: 90-percentile as new average price ? - Etown (1740)

[...] I voted no because I am hesitant to support anything that would expedite the race to the bottom. It's getting more and more difficult to find sets with a large enough [...] (69 months ago, Oct 1, 2018, to Suggestions)

Re: 90-percentile as new average price ? - jx (13)

[...] (Bump) I'm in favor for including median along with average, which is a commonly used measure for heavily skewed price measures like housing prices. I have [...] (46 months ago, Aug 12, 2020, to Suggestions)

8 Messages in this Thread:

 Msg 1 « - Gaston.La.Brick (1841) 69 months ago Oct 1, 2018 to Suggestions
 Msg 2 - Teup (6606) 69 months ago Oct 1, 2018 to Suggestions
 Msg 3 - Gaston.La.Brick (1841) 69 months ago Oct 1, 2018 to Suggestions
 Msg 4 - MidwestBrick (1855) 69 months ago Oct 1, 2018 to Suggestions
 Msg 5 - yorbrick (1185) 69 months ago Oct 1, 2018 to Suggestions
 Msg 6 - Bricks_NW_UK (1366) 69 months ago Oct 1, 2018 to Suggestions
 Msg 7 - Etown (1740) 69 months ago Oct 1, 2018 to Suggestions
 Msg 8 - jx (13) 46 months ago Aug 12, 2020 to Suggestions