Cortex Ratio Analysis

The ratio compares the cortical surface area observed in an assemblage to the amount expected if all the stone present had been reduced in place with nothing removed or added. A value near one indicates a complete, intact assemblage. A value below one means there is less cortex than expected, so cortical pieces such as early flakes or cores were taken away from the site. A value above one means there is more cortex than expected, so cortical material was brought in. Douglass and colleagues used these deviations to infer how stone moved across the landscape, making the ratio a direct measure of artifact transport rather than just reduction stage.

The expected cortical surface area is derived geometrically from the assemblage's volume by assuming the stone originally took the form of nodules of a particular size and shape, since surface area scales with the two-thirds power of volume. If the assumed nodule is too large or too small, or the wrong shape, the expected cortex value shifts and the whole ratio is biased. Douglass and colleagues therefore estimate nodule dimensions from the largest cortical pieces and from local raw-material sources, and good practice runs the calculation under a range of plausible assumptions to check how sensitive the conclusion is, rather than trusting a single estimate.

Debitage analysis classifies and quantifies flaking debris to infer reduction stage and technique, often using cortex on individual flakes as a stage indicator. Cortex ratio analysis takes the same cortex data but aggregates it across the entire assemblage and compares the total to a volume-based expectation, producing a completeness index rather than a stage description. The two are complementary: debitage analysis tells you how the stone was worked, while the cortex ratio tells you whether the assemblage you are studying is the whole product of that working or a transported fraction of it. They are commonly applied together to the same assemblage.