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<p>[QUOTE=&quot;calcol, post: 2453013, member: 77639&quot;]As numerous folks have pointed out, grading is subjective, so accuracy can&#039;t be measured.&nbsp; The only possibilities are statistical measures of consistency within services, among services, and with time.&nbsp; Statistical measures can be used because the results are expressed numerically (1 to 70) and sometimes with a secondary categorical classification (for example, BN, RB, RD). </p><p><br /></p><p>Good luck on getting data about variation among graders within a service.&nbsp; Curiously, back in the days of ANACS photo-certificates, the opinion of four graders for obverse and reverse were listed on the certificate.&nbsp; The closest we can do today is to send the same coins repeatedly to a service a number of times in a short span and measure the variation in grades.&nbsp; However, for all we&#039;ll know, the same grader may have graded it each time.&nbsp; So we couldn&#039;t know if we were measuring variation among&nbsp; graders or variation within a single grader. </p><p><br /></p><p>Comparison among services would be straightforward.&nbsp; Send the same group of coins to each service in turn and compare the results.&nbsp; All should be done within a short time span.</p><p><br /></p><p>Establishing variation over time can be done in several ways.&nbsp; The one way would be comparison with one time period with another; the first ten years of grading versus the last ten years of grading, for example.&nbsp; The other way is trend analysis, which evaluates whether there is a significant trend over a time span.</p><p><br /></p><p>There would have to be separate studies of each coin type and well-thought-out statistical plans.&nbsp; The major grading services have probably performed some of these studies, but aren&#039;t likely to release the results.&nbsp; They could hardly be called unbiased investigators in any case.&nbsp; Perhaps a collector or organization with sufficient resources may fund the studies.</p><p><br /></p><p>The results and conclusions have to be used correctly and cautiously.&nbsp; For a particular coin type, one service may grade higher than another on average, but variation has to be considered.&nbsp; Typically variation gets expressed as to whether the averages differ significantly at some probability level.&nbsp; Typically, this is 95% in most scientific studies.&nbsp; But, for a collector, knowing that there is a 51% probability that one service grades higher than another might be good enough.</p><p><br /></p><p>The results wouldn&#039;t necessarily provide a clear guide as to whether one service is better than another for a collector submitting a single coin.&nbsp; For example, suppose service A&nbsp; grades Morgan dollars significantly higher than service B, but the variation within service A is greater than service B.&nbsp; You have one dollar to send in.&nbsp; If you were sending 100 Morgans, service A would be the choice, but for your one dollar, service B, which is more consistent, might be the way to go.</p><p><br /></p><p>Finally, for many folks, market value is really important, and a statistical study of market valuation of grades of different services is completely different from one that looks only at grading variation.</p><p><br /></p><p>Cal[/QUOTE]</p><p><br /></p>

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