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<p>[QUOTE=&quot;Suarez, post: 3525031, member: 99239&quot;]A few years ago I tried to tackle this problem scientifically so as to come up with a system was at least somewhat based on factual data rather than opinion and conjecture. To do this I found it necessary to brush up a bit on statistics which to me is about as fun as poking myself in the eye. Anyway, I published the results of this investigation as a blog entry at <a href="http://dirtyoldcoins.com/Roman-Coins-Blog" target="_blank" class="externalLink ProxyLink" data-proxy-href="http://dirtyoldcoins.com/Roman-Coins-Blog" rel="nofollow">http://dirtyoldcoins.com/Roman-Coins-Blog</a> (third post down)</p><p><br /></p><p>The gist of it for those who have no interest in reading technical specs is that there are two major types of &#039;rarity&#039; as concerns numismatics. There is <i>absolute </i>rarity which gives a precise number; ie., the mintage. Unfortunately, while this helps settle the matter for modern coins it doesn&#039;t really help in the case of ancients since those records have long disappeared. However, to our aid we can study <i>market </i>rarity which is nothing more than tallying categories of coins from the marketplace and compiling the results. Using simple algorithms from inferential statistics you can then develop prediction models to come up with the likelihood of any one type of coin showing up at auction over a given period of time. If the model is successful then you can apply rarity labels that are useful.</p><p><br /></p><p>But it&#039;s also important to talk about <i>perceived </i>rarity which, of course, isn&#039;t a really an actual definition. For Roman coins, as pointed out several posts earlier, mention Pescennius Niger or Didius Julianus and the average Roman collector immediately thinks of them as downright rare. They&#039;re really not, comparitively speaking. They&#039;re more common than, for example, a Hannibalianus or Flavius Victor but since these last are ugly little bronzes of no special historical significance in commercial numismatic marketing at least, they don&#039;t have the same appeal and this keeps their prices artificially low (or, conversely, those of P. Niger and D. Julianus artificially high) relative to their real rarity. In other words, sleepers. In a literal sense they&#039;re also very common, or at least available, since at any moment you can find them for sale on offer from many dealers and auctioneers. </p><p><br /></p><p>Anyway, that&#039;s not the point. None of this really matters semantically when defining rarity. When it comes down to it the only way this term has meaning is when you compare known values. Since mintages aren&#039;t known for ancient coins the best you can do is come up with reliable data and then using that say X is rarer/commoner than Y.[/QUOTE]</p><p><br /></p>

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