Price analysis was based on the statistics and prices of more than 50,000 unique diamond listings available via the Internet during the first week of July, 2004.
3.7.1. Market price adjustment
AGSL graded diamonds with Ideal Polish and Symmetry are often priced about 8% - 10% higher than similar GIA-GTL graded diamonds with Excellent/Excellent symmetry and polish. However this differential fluctuates over time and carat weight ranges; a week later than this survey’s analysis period, equivalent GIA-GTL and AGSL listed diamonds in the 0.6-0.69 carat range averaged out at the same price. The relatively small numbers of these stones, and the niche nature of this business, means the various margins of a small number of vendors can have a large effect on the average price results.
A number of the diamonds in this survey were not graded as AGS 0 by AGS; these diamonds trade at a lower premium to GIA stones. This has been taken into account in the pricing of these stones.
EGL graded diamonds are currently offered within the trade at 9% - 15% lower than the same grade GIA-GTL stones. Our statistics[1] show little (within ±3%) difference in prices for diamonds graded by EGL USA and EGL overseas, although anecdotal evidence suggests a larger differential.
Table 2. An example (using stone # 3) of the method used to calculate the market price comparisons in Table 3.

E.g. stone # 3 GIA EGL
Carat 1.08 1.08
Color H G
Clarity SI2 SI2
Number of stones in database 85 54
Avg. Price $4,248 $3,634
Price difference -14%



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[1] The only way to automatically differentiate listed diamonds graded by EGL USA from EGL in other countries was by the grading report numbers; EGL USA report numbers start with 'LA’, 'US' or '7', or end with 'D'. At the time of this survey there were some 2,500 diamonds in Pricescope database with EGL grading reports that satisfied this condition and about 4,100 listings with EGL reports with numbers that did not. Report numbers were not available for all EGL graded diamonds.