Statistical Analysis Of Key And Semi-Key Mercury Dimes

For background information, I posted a similar thread on Lincoln Cents:

https://goccf.com/t/88992#735292

Now for the Mercury dimes. I thought I would treat these as a single group, and also compare my findings with the current price (as found on numismedia.com for G4.)

From the LWC study: key date z-values were found to be -2.2 and less; semi-keys between -2.2 and -1.5.

To get a z-value, I determine the relative standard deviation from the mean (log mintage) values. The results for the "top 10" Mercury dimes are as follows. My labels for key and semi-key are from the above definitions:

1916-D -3.08 key
1921-D -2.03 semi-key
1921 -1.93 semi-key
1931-D -1.92 semi-key
1926-S -1.78 semi-key
1931-S -1.65 semi-key
1930-S -1.63 semi-key
1931 -1.23
1928-D -1.02
1929-S -0.93

I then compared the price (G4 based on numismedia.com) with these z-values. The graph below shows the log (price) on the y-axis and z-value on the x-axis. You can see a trend and you can also see a premium only for some of the semi-keys. The 1931-S and 1930-S do not have a premium, although they are fairly rare.



Comments? Thanks for reading...