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Old 09-27-2009, 02:28 AM
rasiel rasiel is offline
Join Date: Sep 2005
Posts: 276
Default ebay rarity vs. cost graph

the topic of cost versus rarity is interesting to me. while the majority of roman imperial coins are roughly commensurate in their cost relative to their market rarity there are a few examples that don't follow this rule.

when you have a relatively ample supply of coins for a given ruler, or a given issue, but the perceived rarity is high the supply-demand balance goes out of whack and the prices stay higher than normal. "normal" being the operative word in a clinical formula. the conclusion to draw isn't that you're being gouged so much as the realization that costs are not purely dependent on rarity but are also heavily influenced by desirability. think of otho or tiberius denarii which are quite common but aggressively bid on by collectors.

the opposite situation is the sleeper coin that is cheaper than it should be considering its scarcity in the marketplace. good examples of these are the 4th century empresses most of whose ae denoms are cheaper than they should be all other things considered.

attached is a crude look at a pseudo-random selection of rulers sourced from from coinvac.com to make into a graph chart. the vertical axis is the number of coins present in the database from sales over the last two years while the horizontal is the cost per coin averaged over the number of specimens. while the bulk of these fall within an expected band running down the middle, as would be expected in a one-to-one correlation between market value versus supply and demand, a few fall significantly out of the curve.

the closer to the upper left the ruler is, the more a bargain and those falling below the imaginary diagonal less so the farther away they are. given that the total number of coins sampled in this study is a little over 36,000 it would seem that of the chosen rulers tetricus II (with only 224 @ avg. price of $13) and mariniana (35 @ ~$150) are good bargains relative to the rulers closer to the bottom right.

i said the graph is crude. it does not take into consideration certain factors like what if a few odd aurei of hadrian are dragging the cost downwards or maybe some are particularly high grade and so on. it is just a "snapshot" to give one an idea. a more careful selection could refine the analysis to spotlight some real dogs and sleepers. also, a tool could be made to quantify the deltas between market rarity and average cost to provide even more dramatic at-a-glance differentials.

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Old 09-30-2009, 12:22 AM
mrichter mrichter is offline
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Join Date: Sep 2005
Posts: 170

Very interesting. I would really like to see a similar graph for some specific coins, as I mentioned to you off the forum, like the Tribute Penny. Alexander Tetradrachmas and Athens Tetradrachmas would also be interesting to see in this format.
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