Finally, recognizing the skewed, non-sinusoidal shape of the rhythms in
the error data, we proceeded to fit a combined 24 h fundamental and 12 h
harmonic sinusoidal curve (Brown & Czeisler, 1992; Kerkhof & Van
Dongen, 1996) to the skill-based and total error data, so as to obtain a better
estimate of the circadian timing of the minimum and maximum number of
errors. This analysis indicated a peak in total errors shortly after 02:00 h,
and a peak in skill-based errors between 02:30 and 03:00 h (Table 2).