If you shoot a 5-shot or 10-shot group, that group's size is normally measured using extreme spread. This gives you a single value to compare against other groups.
In this video, we look at a second method to compliment extreme spread called shot distance to centroid. Check out this video to learn more about this method. This approach is also called the Group Mean Radius and you can learn about it by visiting https://www.researchgate.net/publication/45849904_Statistical_Methods_for_Determining_Optimal_Rifle_Cartridge_Dimensions
Links:
Does Annealing really change brass? https://youtu.be/fBBL2d8otRg
Extreme Reloading Season 8 https://youtube.com/playlist?list=PL_KBTsQIm0U6kUJkOnF6EyEVziYkmZo40