Analysis of Covariance (ANCOVA)

ANCOVA is probably one of the most frequently used statistical analyses, but also simultaneously one of the most frequently misapplied. There are some good papers to help people understand the pitfalls and limitations of the procedure. My favourites include:

Miller, G. A. & Chapman, J. P. (2001). Misunderstanding Analysis of Covariance, Journal of Abnormal Psychology, 110(1), 40-48.

Maxwell, S. E., Delaney, H. D., & Manheimer, J. M. (1985). ANOVA of residuals and ANCOVA: Correcting an illusion by using model comparisons and graphs. Journal of Educational Statistics, 10, 197-209.

I had these papers in mind when I prepared these videos demonstrating how to do an ANCOVA. I hope you enjoy them and learn a thing or two about performing and interpreting an ANCOVA.

(NB: go directly to my youtube channel to adjust the size of the video: http://www.youtube.com/user/how2stats)

http://www.youtube.com/watch?v=_uYASFVUNpQ

NB: The results of the analysis in this series found that males appear to have larger cranial capacities than females, even after controlling for the effects of body size. However, it should be important to emphasize that research has found that there are little to no general mean differences in IQ between males and females. Furthermore, there is neuroanatomical research to suggest that female brains appear to have more neurons per cubic cm than male brains. Thus, the difference in cranial capacity/brain size between the sexes may be counteracted by the differences in neuronal density.