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Is The Numista Rarity Index Any Accurate?

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Author Previous TopicReplies: 3 / Views: 236Next Topic  
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 Posted 02/17/2021  03:11 am Show Profile   Bookmark this topic Add MichaelSH to your friends list Get a Link to this Message
Been wondering... Literally so much coins on the site have a high rating.

Is it accurate or is it because people haven't entered their collections in their accounts?
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United States
11477 Posts
 Posted 02/17/2021  04:38 am  Show Profile   Check spruett001's eBay Listings Bookmark this reply Add spruett001 to your friends list Get a Link to this Reply
I find that statistic to be minimally useful. It doesn't necessarily correlate to the overall actual scarcity of the coin and yes, is dependent on members adding those coins to their online "collection" so it's doubtful it's even accurate within only the Numista community.

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Russian Federation
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 Posted 02/17/2021  04:57 am  Show Profile   Bookmark this reply Add january1may to your friends list Get a Link to this Reply
As I understand it, the Numista Rarity Index is exactly accurate (modulo some low-level timing troubles) in terms of how rare the type in question is among Numista member collections. Numista audience skews French, so French-associated coins tend to have lower ratings and coins that French people are less likely to collect tend to have higher ratings.
This also conflates rarity with interest in general; types that aren't, technically speaking, rare but also aren't collected often (by English/French speakers, at least) would get high rarity ratings.

In addition, the ratings are intrinsically type-based, so a common type coin has a low rating even if the type is full of rare dates, and type granularity has a big impact on the rating (e.g. many 18th and 19th century Russian coins are subdivided into "types" by mint, which makes their rarity ratings artificially higher; for some other series, particularly among ancients, the situation is even worse).

There are probably also many cases (especially among ancients) where the relevant types just hadn't been listed yet back when most members were entering their collections. There's a long-ongoing project on listing all the Roman types (currently up to Macrinus, 218 AD), and after a few years we'd probably see the Roman coin rarity ratings stabilize a little as comparatively common types get the appropriate amounts of collectors entering them (though most types will still be 100/97/95, obviously).
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 Posted 02/17/2021  05:03 am  Show Profile   Bookmark this reply Add MichaelSH to your friends list Get a Link to this Reply
Thank you for the information guys!
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