Reference
Glossary
The terms used across the Caratlytics methodology and the Diamond Price Index, defined as this site uses them.
- Caratlytics Score
- The 0 to 100 composite measure assigned to a diamond listing: Quality x 0.35 + Value x 0.30 + Certification x 0.20 + Market x 0.15, with the weight of any unavailable pillar redistributed.
- Quality score
- The gemological pillar: a weighted sum over up to nine graded components (cut, color, clarity, proportions, polish, symmetry, fluorescence, culet, girdle) divided by the fixed maximum weight of 100.
- Value score
- The price pillar: where a listing's price per carat sits against its category baseline quartiles, plus carat threshold effects and cross-retailer price position.
- Certification score
- The trust pillar: laboratory reputation, weighted data completeness across 18 fields, and certificate availability, subject to an integrity gate.
- Market score
- The market pillar: cross-retailer verification, 30 day price trend, price stability and savings potential, computed from live listings and retained price history.
- Grade band
- The fixed mapping from raw scores to consumer grades: A+ 90 to 100, A 80 to 89, B+ 70 to 79, B 60 to 69, C 50 to 59, D 0 to 49.
- Data coverage
- The share of weighted gemological evidence present on a record. Below 60 percent, no quality score is issued.
- Category baseline
- The daily recomputed price statistics (quartiles, median, interquartile range of USD per carat) for a category of comparable stones: same shape, carat band, color band and clarity band.
- Price per carat
- Listing price in USD divided by carat weight. The unit in which baselines, the value pillar and the price index are computed.
- Interquartile range (IQR)
- The distance between a category's first and third price quartiles. The value pillar scores percentile position within and beyond this range.
- Cross-retailer match
- Two or more retailers listing the same physical stone, identified by laboratory and certificate number. Matching powers verification, price position and the spread statistics.
- Magic weights
- Carat values where retail prices step up because demand concentrates on round numbers: 0.50, 0.70, 0.75, 1.00, 1.50, 2.00, 2.50, 3.00, 4.00 and 5.00 carat. Buying just under a magic weight is rewarded by the value pillar.
- Integrity gate
- The certification rule that caps a record at 30 when it claims a certificate and laboratory but lacks color or clarity data.
- Coverage gate
- The quality rule that refuses to issue a score when present component weights total less than 60 of 100.
- Pinned exchange rates
- The fixed currency conversion table used to express all prices in USD as a stable unit of account. Pinning keeps score and index movements attributable to retailer repricing rather than currency markets.
- Systematic sample
- The index sampling rule: one listing in ten, selected by listing identifier, each contributing its latest observed price in the calendar month.
- Price history
- The retained record of every observed price for every listing, which powers the market pillar's trend and stability components and the price index.
- Fancy color diamond
- A diamond graded on the fancy color scale (Faint through Fancy Vivid) rather than the D to Z scale. The quality pillar reweights for fancy stones: color 30 points, clarity 8.
- Lab-grown diamond
- A diamond crystallised in a laboratory rather than mined. Chemically identical to natural diamond, certified by the same laboratories, and tracked as a separate segment throughout the methodology and the index.
- Listing
- A specific stone offered by a specific retailer at a specific price. Value and market scores attach to listings; quality and certification scores attach to the stone.