Eight months ago I have reported on my duplicates list the Rarity Index. Almost all coins were in line with other similar index and with number of collector offering to swap the coin.
During these holidays I check them again to updates values. With my surprise most of them are completely changed of 10 to 40 point!!! Although in many case total number of collectors getting the coin to swap were the same.
I should like to know if it is changed algorithm to calculated index, if somebody has decided to reduce all index or some other reason.
It is not possible to have a value under 50 for a coin type if no collector get it to swap, it means that you can't find it in Numista, it is at least a bit difficult to find also outside. And most coins are now between 0 and 50
Moreover I should like to know formula to calculate him. So all members can have a right opinion of it. May be that their contribution could be useful to improve it.
About 999 peoples, how many people are coins collectors?
However this is an index from 0 and 100 calculated within Numista collectors and an index is not influenzed by total number of collectors and is not possible that all coins go in the same decreasing direction.
If only two collectors on 1000 own a coin to swap and now they remain two on 1500, there is no reason to decrease its Rarity index. Enrico
引用する: enrico... changed of 10 to 40 point!!! Although in many case total number of collectors getting the coin to swap were the same.
I believe, when people add and remove coins from their collections, the rarity index changes. It does not mean the coins are all available for exchange, it just means they are or aren't in people's Numista collections. Number of new members, with or without a specific coin, would also contribute to any +/- changes.
Here are a couple of coins many people have and no one is willing to exchage, Rarity index 68, 69...
I agree to you, rarity index is not an absolute index, it regards only Numista population of collectors so their variation in total number and their type of coins owned contributes certainly on the index. But why only in decreasing and in a strong way?.
Perhaps algorithm used is not right. Is it time to check it?
If on your examples previous index would have been respectively much more greater than now with the same 0 and 4 people who want to change these coins, what do you think? That suddenly many Numista collectors found or bought these 3 coins or many collectors without these 3 coins go out from Numista or perhaps algorithm to calculate index is not good enough?
I should like to know the meaning for Numista of values of rarity index as 100, 90, 80, 50, 30 and 10 for a certain coin type. How many collectors or % collectors get him in collection or to swap.
Sorry for my bad English but I hope to have been understood.
Pick a coin that is rare and shows 100, add 1 or 100 of them to your Exchange list or Numista collection and you should see it drop to 97. Remove it from your Exchange list or Numista collection and you should witness it go back to 100. Proof that Rarity does go up.
May be we have a misunderstanding. I have been very glad about introduction of a rarity index. It is a welcome and useful tool to evaluate difficulty to find a missing coins within Numista. And roughly perhaps also in other numismatic club if no too much different in country population of their member.
No discussion about increasing and decreasing with rarity. If you add a coin you have index decrease, if you remove index increase. But this behaviour doesn't means that formula to calculate it will be right.
Initial values calculated about one year ago were more right than actual values.
Now single values are too low and no more in line with other similar rarity index (and a bit also with catalog evaluations).
引用する: enricoBut why only in decreasing and in a strong way?
引用する: enricoNo discussion about increasing and decreasing with rarity.
Ok, now I am confused.
引用する: enricoBut this behaviour doesnt means that formula to calculate it will be right.
Thank goodness I'm not a member on a math forum. I'm going to stick to coins. Formula does not really interest me. There is a Dr.Math here, as well as a Numista statistician, Cerulean. Maybe they wish to add a word or two.
Traditional rarity indices, the kind that were published by numismatic agencies and auction houses, are based on long-term dealer trends with that particular coin. These types of rarity indices were static and unchanging.
Numista's rarity index is a new and different type of rarity index. It is a relative rarity value determined directly by collectors (specifically among Numista members). The Numista rarity value is dynamic, intended to change as more users report owning a type of coin. As the number of Numista users grows, and as those users expand their collections, the rarity index will go toward zero, as it should. If more people have a coin, it isn't as rare.
I can understand the confusion the original poster has, if he thinks the dynamic Numista rarity index is supposed to be a fixed and unchanging value like a traditional rarity index.
I try to answer you in my language hoping you have a good translator otherwise we don't understand each other:
Nessuno pensa che l'indice Numista sia un indice fisso ed invariabile nel tempo. Infatti dipende da molte variabili ma non dal numero di collezionisti iscritti al club, il numero totale migliora l'affidabilità del metodo usato non il valore dell'indice.
Dipende invece dal livello dei collezionisti e dalla sua distribuzione nazionale e dalla quantità degli scambi, difatti lo stesso indice applicato ad una altra popolazione può dare risultati diversi ed avere un andamento diverso nel tempo.
Nel tempo un aumento di collezionisti dovrebbe aumentare il valore assoluto dell'indice perchè principalmente essi saranno nuovi collezionisti. Nello stesso tempo però i vecchi collezionisti riusciranno a migliorare il livello della loro collezione facendo diminuire il valore dell'indice. Questi due principali effetti potrebbero tenere inalterato il valore di molti indici, alcuni cresceranno e altri diminuiranno.
L'unica conseguenza anomala è che come è successo a Numista, gli indici di tutte le monete diminuiscano in modo così significativo in breve tempo.
No one thinks that the index is an index Numista fixed and unchanging over time. In fact depends on many variables but not on the number of collectors club members, the total number improves the reliability of the method used, not the value of the index.
However, depends on the level of the collectors and its national distribution and the amount of trade, in fact, the same index applied to other people may give different results and have developed differently over time.
Over time, an increase of collectors should increase the absolute value of the index mainly because they are new collectors. At the same time, however, the old collectors will be able to improve the level of their collection by decreasing the value of the index. These two main effects may keep unchanged the value of several indices, some grow and others decline.
The only consequence is that as abnormal has happened to Numista, the indexes of all the coins decrease so significantly in a short time.
More than 30 new users joining Numista each and every day, with the new listings of coins they bring. It's no wonder that Numista's rarity index changes so fast!
For new emissions rarity index decrease sharply because other collectors find them but no for older emissions because new users are mainly novice so they decrease percent of collector population who get a certain coin, specially coins with high rarity index! Enrico
