How many members have this coin?
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On Numista, is there a way to tell the number of members have a particular coin (not just for swap)? This would help a newbie like myself to tell whether a coin is common or rare and help me in my swapping. While I know a little bit about the series of coins that I collect (key dates etc.), I know little or nothing about other coins (for e.g. coins from Greenland or Swaziland). It may not be a very accurate gauge if there are no members who collect them but at least we could get a general idea. |
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There is a way. I used it myself recently. The link is ... http://en.numista.com/echanges/index.php The way I found it is on the left of most pages are the sections ... The catalogue / Exchanges / Your account and I went to Exchanges and clicked on Start a swap. And yes, I know that you do not, to start with, intend to start a swap, but that is the place to look. Then go to the top of the page that appears, and use the arrow on the right of the Countries box to choose the country you are interested in. So for example, clicking on Greenland the list starts like ...  I see you asked 'the number of members have a particular coin (not just for swap)' so all that is just for exchange/swap - so maybe you already know how to find that information. Shows how hard Greenland is also - only four coins shown, with only two collectors having them for exchange. Not sure then how to find what is in a collection - which I think is what you wanted, so maybe I jumped in too quick.  
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Hi Zac I was trying to skin this cat a bit differently. For example if I was offered a UK 50p in swap and went to the page for that coin - I would want to know the number of members who have an entry on that page (numbers about each date line would be even better but that might be a huge task). Not "who" owns it but how many would give me a quick idea on what to offer in swap without doing a whole lot of research. Again this would not be an exact science but will give me a general feel for the availability. |
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Ah yes - I see now. I don't think there is currently a way to see that. Perhaps it can be added in the future. The information (of what coins are in a collection and not for exchange) is on there somewhere already. I mentioned in an existing topic recently, that the only way I perhaps would know if I had a scarce coin was if there was a comment in the year list on a particular page, or at least had a mintage figure. So in the absence of either of those two how would a member know the common-ness, if they were putting a coin they have up for exchange; whereas with such information as you suggest then they might want to keep it in their collection instead - or ask for a better than 1/1 swap. |
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This would work for swaps or when we are at a coin shop or coin show and see something interesting, we could do a quick check - by coin and by date - that would give us a feel for availability. The data exists already, it would be a matter of adding a column to the date row with "# owned by members". |
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Quote: @josephjk
Would not the number of people offering it for swap give you an idea of scarcity? I can tell you that the Kew Gardens commemorative 50p is rare, but very few non-numismatic people (Muguls?) in the UK know it. They retail for about £6 currently, and were only circulated last year! Bet no one has one on offer for swap, mine are locked away as an investment for my daughter (I cant afford real investments like gold/silver). Matt |
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That is a great example - if I saw a coin that was well owned but very few were up for swap - that would be another way to alert me that a coin is more sought after. |
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Quote: @josephjk
And if you saw a coin that very few people owned? How many collectors do you know that throw away the only example of a coin they own? Very few people own coins from Greenland, that's because they are scarce. Lots of people are offering French 20 centimes for swap, that's because they are common. Very few people are offering UK Olympic 50ps for swap, that's not because they don't own them, its because they are so sought after. Check the number of people offering a coin for swap, that will alert you to its *real* value to collectors (or at least those who are members of Numista.com), irrespective of book prices, mintage figures or composition. Matt |
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Hey guys, As an admin, I am able to see how many people own a certain coin. For example, I can see probably half of the people who own a 20 Centime coin from a certain year, due to the fact that there are so many people who own the coin I can't see everyone. But if I looked at a coin from Cambodia, the number of people owning the coin would be little to none. You'd be surprised with the number of people owning some coins. There are probably some 20-30 owning each of the cast and copper cash coins. Fijian coins have very few owners (although I have a BU 1977 20 cent). Ask me about a coin, and I'll look it up and see how many people own it.
SmartOne |
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"And if you saw a coin that very few people owned? How many collectors do you know that throw away the only example of a coin they own?" If it was a common coin and I could get it it later (like a US quarter or dollar ) - I'd give it up in a heartbeat to get a coin from a series I'm collecting The number of coins up for swap is a good way to tell if a coin is common but I'd rather have more data than less to make a decision. If a large number of people owned a coin, whether it was up for swap or not - stands to reason I could find one. |
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Quote: @josephjk
Somebody asks for this every six months. It's time this got implemented. |
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Hello, I don't want to publish the exact number. I consider this as private data, especially when just one or two people own the coin. But I'm seriously considering a rarity index based on the number of members owning the coin, the number of members offering the coin, the total amount of owned coins, and the total amount of offered coins. However, many coins are not owned by anyone, but not necessarily because they are rare, but because they don't interest anyone. |
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I think a rarity index would be a great idea. I'm sure that some coins will be mislabeled by the system due to lack of interest or because they haven't been widely circulated when they are first released, but I think that this issue will be easy to overcome as long as it is known that the system is just based on data entered by members and is not necessarily an indicator of over all production of the coin. |
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Quote: Xavier
Good idea. Just how one should define an algorthim for a rarity index should prove an interesting challenge! As I understand it one has the variables of: Mintage, ownership, and availability for swap Mintage must be a consideration, if there are very few in existence there can by nature only be a few owned by members. Matt |
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Hello, I just put in place the rarity index. It's recipe is a bit complex, but I'm sure it can be improved. Feel free to report any coin you consider as under-indexed or over-indexed. |
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Xavier, Just spotted the rarity index. Again a super addition. May I take this occasion to say Happy New Year to you and well done. |
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Thank you very much for the new addition! |
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Here is my answer to Matt's question. The recipe of the index is based on the following ingredients: - number of coins claimed by the members - number of members claiming to own the coin - number of coins available for swap - number of members offering the coin for swap The index is based only on Numista members collections. So, if a few members decide to buy some numismatic rarities such as the Lundy puffin, then it will rank lower than a junk non circulating coin. Although the later can be easily bought at a cheap fixed price, it will be considered as extremely rare if no Numista member decides to buy it. |
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Hi Xavier, Can you elaborate on the second one - "number of members claiming to won the coin" Where does that data come from? thanks |
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My mistake. I meant "who own the coin". I corrected the initial post. |
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Never mind - I just realized the "won" was a typo! For a moment there, I thought you had psychic powers! And you fixed it while I was typing! thanks again! |
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Okay, thanks Xavier. I wonder if the rarity index may be better as 100 - % of members claiming to own said coin eg: 100 - (o/n*100) where o is number of members claiming ownership and n is the total number of recorded members. Thus, if we have 12500 members, and 75 members own a particular coin, then 0.625% own that coin, negating that to give a rarity ranging from 0 to 100 gives 99.375 (pretty rare) And if 10,450 own a particular coin then we get 87.08% owning a coin, which negated gives a rarity index of 12.92 (pretty common) and if we have 11,999 owning a coin then we get 99.992% owning the coin, which negated is 0.01 which is common as a French ten centime! I say this because while many members may own a common, but valuable coin (say something silver) they may not offer it for swap, while a rarer coin in base metal may be offered for swap in larger quantities, and could skew the figures giving the impression that the rarer coin was actually more common than it is. The current rarity index gives the impression that more than half of Numista members own many of the UK Olympic 50p series coins, and I don't believe that for one minute! While they have been available to buy from the Mint for a while, some have only been released into circulation these past few days! Matt |
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Hmm i've added the roman "carisius" coin that i have...and that makes the coin rarity 89...and if i delete the coin from my collection it's 100 so im the only one who has the coin...and the rating 89 is a bit small i guess. |
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Quote: kommodore
So does this support my algorithm? If you are the only member with this coin, then I should say it has a rarity of 99.992 (by my algorithm with you as the only one of 12,000 members owning the coin), and if you delete it then its rarity changes to 100. Which sounds aabout right, I think? Matt |
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Yeah it's better then rarity 89...in the actual algoritm i guess if 5 people add the coin the rarity drops to 50-60 |
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This might almost be too much to ask but can this be done by date line? Some dates being more rare than others...again I realize there are space constraints |
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I would suspect that adding it by date would be a logical step once everything is set and the bugs are worked out. I would also like to see the information added to the swap page as a total at the bottom (like the weights). It would be handy to have a head to head comparison while choosing coins for a swap. |
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Hello, I've changed the algorithm, si it's less sensible when the first few people add the coin in their collection. @josephjk, ctucker, I fear that a rarity index by date wouldn't make sense for many coins, since Numista doesn't have enough data. About half the dates in Numista catalog don't have a single member claiming to own it. Matt Probert, I don't like your algorithm for three reasons: - It causes the index to be very high. All indexes would range between 99.88 (for French 10 centimes) and 100. - It doesn't take into account the availibility of the coin. - In my opinion, a coin owned by 1500 members or just 750 members are equally "rare". They both should have a very low rarity index. With your algorithm, the second coin is two times more rare. |
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Quote: Xavier
Fair enough if you don't like my algorithm (its your site, you do as you wish). Though I don't understand your logic as presented (a coin owned by n people is no less common than one owned by 2*n people???) Whatever you have done to the index, it seems to be more reflective of actual scarcity now. Matt |
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Despite my fear of further upsetting Xavier (I really am only trying to help, I'm not just being a smart arse for the sake of it), might I offer one final word of caution? Numista is still taking into account the total number of coins available for exchange. This enables me to change the rarity index for a coin by amending the amount I offer available for swap, so while I may have 23 examples of a particular UK Olympic 50p, if I present 22 of them as being available for swap the rarity index is lower than if I only offer 1 for swap. Thus, I can manipulate the rarity index by simply reducing the quantity I have available for swap to 1, even though I have more, so as to improved the coins rarity index and thus demand a better deal for swapping that coin. Perhaps if the quantity available for swap was based not on the total quantity, but on the number of members offering any of that coin for swap? Then a member wouldn't be able to manipulate the figures, as it wouldn't matter if any individual member was offering 1 or 100 examples. Matt |
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Hello, first I wish a Happy New Year to all of you. I was just experimenting with the rarity index this morning, and as only I have certain Albanian coins for swap, I changed the number of a certain type of coins, and the rarity index rose, but only by 2 or 3 points. 5 Qindarka 1969, I have 10 for exchange, and has an index of 63, while when I put just 1 coin for swap index goes to 65, I find this change not so significant, 2-3 percent for 10 coins is acceptable. And I like this index, as future swaps could also be based on this index rather on KM values only. Albanian Communism era coins are not accordingly priced in Krause just because they are Aluminum and the mintage figures are not published, but they are uncommon coins and quite sought after, because Albania was a closed country and very few coins "escaped" abroad, and the mintage was low, even though not published. Aluminum coins were minted in China. So I congratulate Xavier for this nice and valuable tool. |
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Quote: lidianb
The rarity index, as it stands, is weighted. So the quantity any individual has for swap is more relevant with coins with a higher rarity index than those with a lower index. I agree its a nice feature, and I don't want anyone to think I am complaining. I was just trying to assist Xavier to improve a feature which is currently "under test", by which I assumed (perhaps wrongly) that he wanted members to test it and make constructive suggestions. Matt |
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I tend to lean toward Matts point of veiw on one part of this issue. An individual shouldn't be able to influance the stats by listing or subtracting a couple coins. Maybe a one vote per person would work better(based on how many members own it, and how many members have it for swap, but not how many a member owns or has for swap). But even as it is now, I think it is a good addition. |
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Quote: Matt Probert
Yes you are right here... And i like the idea to have an index per year not per coin. |
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Hi, Some thoughts on the rarity index: First, it is nice to see new feature in New Year! Thanks Xavier. I think it could be nice to see the equation you use to calculate the index - at least temporairly during test of it. It may help to understand it better and may be suggest some improvements. I have already manipulated rarity index of some coins by reducing number of them offered for the swap :-) The index has generally rised about 2-4 points as mentioned earlier. So I think the quantity offered by single user should not be taken into account. People having 10 coins of the same type for exchange can keep constant number of 1 without bothering with a change of the number after each swap. However, for me it is important to see if someone has one or more coins for exchange. The rarity index which uses the quantity of offered coins can cause some big changes on the face of Numista swap system. Thanks, malol |
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I think the rarity index is a great tool. Would it be possible to also put it on the list of coins you get from the search page and the list of coins you get when you start a swap, so you don’t have to open each coin to see the rarity? |
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Then there might have to be more than one index...there might be more than one coin that is rare in a single sheet but at the same time it might be more than one rarity (No mintmark) for example and also under the same sheet (a thin planchet). Haven't explained it well...sorry. |
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Any chance on the Your Coins sheet we could have the rarity index displayed:  Just to say this isn't me saying woohoo like I got a 94, it is just a token...this is just on the top of my list as an exemplar. |
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Hello, I just changed the algorithm, so as to take into account only the number of members and not the number of coins.This way it should be more difficult to manipulate the index, and the index should not have any impact on the behavior of members when entering their coins to swap. The rarity index of most of the coins didn't change with the new formula. |
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I would beg to differ. Many entries of rare coins have their numbers much higher, such as some coins from Demerary and Essequibo.
SmartOne |
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Hmmm, I just added two NAAFI tokens as issued to British forces in Afghanistan. Before adding the quantity of these I own (1 of each of two different denominations) they both had a rarity index of 100 (of course, they were unknown to the database). Adding my owned quantity of 1, reduced the rarity index to 97. 97 seems a bit low of an index for a unique coin (not really unique, but Numista only had a single one recorded at the time it generated the rarity index). This would indicate that for any actual coin owned by a member, its maximum rarity index can be 97, 100 only relating to coins not owned by anyone. I just point this out in case it has slipped by unnoticed. It may be what you wish to achieve, or it may not. Matt |
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Okay, I like the rarity index. But I have a query about it. It appears that the rarity index is very linear, a coin catalogued by zero members registers a rarity index of 100. A coin catalogued by one member registers a rarity index of 97, and as the rarity index diminishes towards zero, so the rarity index steps reduce much slower, requiring more members to catalogue an example before the rarity index value reduces. This leads me to wonder how the rarity index actually reflects a coins scarcity among the Numista population. Can Xavier provide some insight, please? How does a rarity index of say 50 relate to the proportion of Numista members having catalogued a coin? And how about other values? Some idea of a scale should be very helpful, other than a glib "0 is common 100 is rare", because of the linearity of the index this statement means nothing in real terms. While, purely as a hypothetical example, "0 Extremely common 10 Very Common 30 Common 50 Slightly scarce 70 Scarce 90 Rare 100 Ultra rare" Would enable me to understand what the rarity index actually means in real terms. A Numisdoc on this subject would be very helpful. Matt |
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Just wondering isn't better if instead of rarity it shows the number of member that has the coin? |
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Quote: kommodore
That was where this thread started back in November, we have moved on since then. Matt |
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Oh ... haven't really read all...
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Hello and happy new year ! A question: Numista has more than 20000 coins in catalogue, really, but I can find a coin which isn't in no one collection ? kind regards
Acid Burn |
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Coins that are known and listed but not owned. |
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Quote: Xavier
does this mean that only 15 members own the French 10 centime coin? I think you only made an exaggeration  so is the 10 centime coin (current index 7) really the most owned coin? Or which one is it, and how many members own it? Currently, the calculation is not linear (opposed to how Matt calls it - linear would be with same distances), because 0 members give 100%, 1 member gives 97%, 2 members give 95%, and the steps become smaller very fast - I just added a coin with 80%, and it was still 80% a possible option would be to set the most owned coin at 0 (say, 1000 members own it), and then make a linear or non-linear way between 1000 members = 0% rarity and 0 members = 100% rarity Non-linearity is not bad - the difference between one and two owners is more significant than a difference between 500 and 501 owners. If the least rare coin os owned by 1000 people, a coin which is owned by 500 people should be given less than 50% rarity. Probably, quantiles could be a good idea, then, 10% rarity means that 10% of all coins are less rare, and 50% means that 50% of all coins are less rare. I'm also curious which coin is the least rare coin that I don't have in my collection - would this be worth being shown to us? |
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Hello! What about make next step and add in the list of swap "Volume of Numista Rarity index" (like TOTAL of Numista Rarity indexs for each coins in the swap). We can see the same for Total weight of coins. So, I think it help for better approach to effect a swap. BR Oleksandr |
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In my search for old or silver coins, one thing I have noticed about really valuable or rare coins is that the scammers and swindlers will put a bunch of really nice, rare, and valuable coins on that they don't actually have. not that there is a way to change that, I just noticed and realize that changes the way its supposed to work. Also I saw a guy who listed a gold krugerrand but in his note, it reads that is a "replica" so that too would effect the Rarity index I also think that people with gold and silver fakes should melt them down. The Rarity index is Awesome. Keep up the good work. |
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Where do you have to look to find this rarity index. it sounds really interesting. |
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The bottom of any coin page. Example page, and screen picture (I added the arrow) ... http://en.numista.com/catalogue/pieces1566.html 
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Thanks I've found it i also see that the bullion value of silver coins is under it. I will now have to go through all my coins and see what my highest rated coin is all adds to the fun on the site. |
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Ok, I agree that RNI is a good device to improve our knowledge about difficulty to find a coin by swap. But it depends too much from collectors population. If tomorrow 20 collectors of Andora or SanMarino will register on Numista, rarity index of many coins of these countries will decrease strongly because they probably own them in their collection and have them in their swap list. At contrary french coins are penalized because they are the greater number of numista collector so it is probabily that they get many french coins. But this is the real situation of this club because NRI is not an assolut index but describe very well club swap situation. If I use it for an italian collectors population it will be wrong for coins of some countries, surely for french and italian coins. And so on. And there are some other parameter who can influence this type of usefull index. Enrico |
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I think that the rarity index is a good addition, I would like to be able to search by it in the advanced search, i.e. >50 or <20 if possible. I'd also like to be able to rank my coins by rarity to see what is rare on the site and what isn't. Keep up the good work
Rory Bergin |
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For example if I was offered a UK 50p in swap and went to the page for that coin - I would want to know the number of members who have an entry on that page (numbers about each date line would be even better but that might be a huge task). Not "who" owns it but how many would give me a quick idea on what to offer in swap without doing a whole lot of research. Again this would not be an exact science but will give me a general feel for the availability.
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