Thursday, February 26, 2009

Dart vs Arrow Points

Recently I have been doing some work related to distinguishing between dart and arrow points and their respective debitage assemblages. The standard discriminant function is that developed by Shott (1997), following earlier work by Thomas (1977). Shott's function uses shoulder width in two separate formulae to derive dart and arrow scores.


where x is projectile point shoulder width in mm.

If the dart score exceeds the arrow score, then the point is classified as a dart point, and vice versa. The method correctly classified 92% of still-hafted arrow points and 77% of still-hafted dart points in Shott's sample.

The method is very useful as a guide to classification. However, the double-formula method is cumbersome. Earlier today I flashed to the obvious fact that the two formulae are simply lines, and the point at which they intersect is the shoulder width that distinguishes dart from arrow points.

The lines intersect at x=19.26. Therefore, points with a shoulder width of greater than 19.26 mm are classified as dart points, while those with narrower shoulder widths are classified as arrow points. This is a quick and easy rule of thumb that can be remembered in the field without having to sit down and do the math.

It's good to simplify.

No comments:

Post a Comment