The GHG rating for ships involves comparing vessels to others of similar size (plus or minus 10% of their Deadweight Tonnage or DWT).
The GHG rating methodology analyzes a ship's performance relative to others of the same type and size. It focuses on how far a vessel deviates from the average GHG emissions for its class. According to the provided information, the "GHG Rating size group is based on the size score, which indicates the number of standard deviations by which a vessel varies from the average for similar sized vessels of the same ship type." This means a vessel is assessed based on how many standard deviations it is above or below the average emission levels for ships of comparable size and type.
