Can we be categorised by our DNA?

Here’s an accessible online post on how genetics (DNA) and ethnic groups relate. Using colours as an analogy, the post and the video do an excellent job in explaining why ethnic differences are socially constructed.

For further explanation around the video, check out the original post: https://www.open.edu/openlearn/science-maths-technology/can-we-be-categorised-our-dna by Kaustubh Adhikari where you can learn how scientist refuse to refer to human “races” despite seemingly conspicuous difference!

Galtung’s AJUS System

Galtung (1967) introduced the AJUS system as a way to classify distributions according to shape. This is a means to reduce complexity. The underlying idea is to classify distributions by ignoring small differences that are not important. The system was originally developed for eye-balling, but having it done by a computer makes the classification more systematic.

All distributions are classified as being one of AJUS, and I have added a new type “F” to complement the ones identified by Galtung.

  • A: unimodal distribution, peak in the middle
  • J: unimodal, peak at either end
  • U: bimodal, peak at both ends
  • S: bimodal or multi-modal, multiple peaks
  • F: flat, no peak; this type is new

The skew is given as -1 for a negative skew, 0 for absence of skew, or +1 for a positive skew. The skew is important for J-type distributions: it distinguishes monotonous increase from monotonous decrease.

I have implemented the AJUS system in my R package agrmt. By setting the tolerance, we can determine what size of differences we consider small enough to be ignored. The default tolerance is 0.1, equivalent to 10% if using 0 to 1. AJUS implemented in R sets a systematic threshold, something we do not do when eye-balling differences.

The tolerance parameter is not a trivial choice, but a test is included in the R package to directly test sensitivity to the tolerance parameter (ajusCheck).

Here are some examples (using the experimental ajusPlot function and tolerance = 10):
plot_
Differences smaller than the tolerance set (10) are ignored.

Reference: Galtung, J. 1969. Theory and Methods of Social Research. Oslo: Universitetsforlaget.