How values are worked out
Every value in Valdro comes from the rules on this page. Method 1.
Sources
- Two kinds of sale count. An eBay listing: a sale with a real eBay listing number (an ebay.co.uk/itm or ebay.com/itm link), a sold date and a price. Each listing is one sale, however often it is found, with the number of copies it sold, which never changes the figure. Each sale is labelled with where it came from.
- A member-recorded price: a sale a member typed, pasted or imported. It counts in that member’s vault. If they choose to share it, it counts in other members’ values too, anonymously, at most one shared price per member per card each month. It never appears in the public price guide.
- Sales on eBay sites outside the UK are converted to pounds at the European Central Bank rate on the day each one sold.
- A web-search result, a search grounding link or any other redirect (hop) link does not count, wherever it leads. Neither does a lot or bundle price for several cards, or a price from a guide or data provider with no eBay listing behind it.
- A sale that doesn’t count stays on the card’s sales list, marked “Not counted” with the reason. It never enters a value, a total, a deal or an alert.
Why: A value is only as good as the sales behind it, so each one says where it came from, and links that only point somewhere else never count.
What isn’t used
- Asking prices.
- Unsold or ended listings.
Why: An asking price is what someone hopes for. Only completed sales show what a card sells for.
Matching
- A sale counts only for the same card (set, year, player, parallel and number), the same grading company and the same grade.
- A sale found to be a different card is removed for everyone, not just for the member who spotted it.
Why: A raw card and a PSA 10 of it are different things to buy, and a wrong-card sale would mislead every member who holds it.
Windows and recency
- The windows are tried in this order: 30 days, 90 days, 1 year, 5 years. The first that holds 5 or more usable sales gives the range.
- With fewer than 5 anywhere, there is no range: 2 to 4 sales show their lowest and highest, and 1 sale shows itself.
- Within a window, newer sales count for more. Each sale weighs 2 to the power of (minus its age in days ÷ the half-life).
- 30 days: half-life 14 days
- 90 days: half-life 30 days
- 1 year: half-life 90 days
- 5 years: half-life 365 days
Why: Recent sales say most about today’s price, but a thin market needs a longer look back to say anything at all.
Unusual prices
- A sale is left out as unusual when it is more than 2 × the interquartile range below the lower quartile or above the upper quartile.
- The quartiles come from the last year’s sales when there are 5 or more, otherwise from 5 years. With fewer than 5, nothing is left out.
- Every unusual price is listed on the card page. A member can put one back, or leave another out; that changes their own value only.
Why: One mislabelled lot or shill bid shouldn’t move a value, and nobody should have to trust a filter they can’t see.
Range and most likely
- The range is the middle half of the window’s sales: the 25th to the 75th percentile, by linear interpolation between closest ranks at index (n − 1) × p (the same as Excel’s PERCENTILE.INC).
- Most likely is the recency-weighted median: sort the sales by price (equal prices, older first) and take the first price at which the running weight reaches half the total.
- When most likely falls outside the middle half, it is still shown as worked out, and the value says the most recent sales are above (or below) most of the window.
Why: A range is honest about how much prices vary; the weighted median leans to recent sales without being dragged by one high or low one.
A worked example you can redo by hand
Eight sales in the last 30 days, so the 30 days window gives the range (half-life 14 days). Sorted by price, with each sale’s weight, 2^(−age ÷ 14):
| Price | Days ago | Weight | Running total |
|---|---|---|---|
| £380 | 2 | 0.9057 | 0.9057 |
| £395 | 5 | 0.7807 | 1.6864 |
| £400 | 9 | 0.6404 | 2.3269 |
| £405 | 12 | 0.5520 | 2.8789 |
| £410 | 15 | 0.4758 | 3.3548 |
| £420 | 20 | 0.3715 | 3.7263 |
| £430 | 24 | 0.3048 | 4.0310 |
| £460 | 28 | 0.2500 | 4.2810 |
- Low end: index (8 − 1) × 0.25 = 1.75, between the 2nd and 3rd prices: £398.75. Rounded down: £395.
- High end: index (8 − 1) × 0.75 = 5.25, between the 6th and 7th prices: £422.50. Rounded up: £425.
- Most likely: half the total weight is 2.1405; the running total first reaches it at £400. Rounded: £400.
- Spread: (£422.50 − £398.75) ÷ £400 = 5.9%, with 8 sales: High.
Shown as: most likely £400, recent sales £395 to £425 · High.
Confidence
- Spread is the middle half’s width divided by most likely.
- A 1-year window is at most Medium; a 5-year window is at most Low.
- When most likely falls outside the middle half, confidence drops one level after those caps.
- A value whose sales haven’t been checked for more than 14 days says so, and doesn’t count as High in your Home total.
- High: 8 or more sales and a spread of 20% or less
- Medium: 5 or more sales and a spread of 35% or less
- Low: everything else
Why: The confidence word tells you how much to lean on the figure before you buy, sell or insure on it.
Rounding and currencies
- The step is chosen by the figure being rounded. The low end rounds down, the high end rounds up and most likely rounds to the nearest step (halves up), so rounding never narrows a range.
- Values never show pence. Sale prices and charges are facts and keep theirs.
- Values show in the app’s home currency (pounds, euros or dollars), with sales in other currencies converted at the European Central Bank rate on the sale day.
- Under £100: to the nearest £1
- £100 to £999.99: to the nearest £5
- £1,000 to £9,999.99: to the nearest £10
- £10,000 and over: to the nearest £50
Why: A value is an estimate of a price, not a price; pence would claim precision it doesn’t have.
Why a value moved
- When most likely moves by 5% or more since you last looked, the value says why: new sales, sales ageing out of the window, unusual prices left out or put back, or a currency move.
- Each cause is tried on its own; the first that explains at least half the change, in the same direction, is named.
Why: A value that changes without a reason is hard to trust.
Known limits
- eBay doesn’t show the accepted price on Best Offer sales, so such a sale can be recorded at its listed price, which may be higher than what was paid.
- Thin markets give Low confidence.
- Private and in-person sales can’t be seen.
Why: You should know where the figures can be wrong.
How accurate it has been
For each sale, the range the method would have shown just before it sold, from that card and grade’s earlier sales, and whether the sale landed inside it. The middle half should catch about half of the next sales; a month outside 35% to 65% is called out. Fewer than 30 scored sales: not enough data yet.
Not enough data yet.
Method version and change log
Every value records the method version it was worked out with. Any change to a rule gets a new version and a dated entry here.
- Method 1: First version: ranges from recent sales, with a confidence level and an as-at time on every value.