Season-by-season summary of 25OHD peaks and troughs.

Half-year periods (columns I and II) are defined equinox-to-equinox (S/S, “spring/summer”; F/W, “fall/winter”). Column III gives the total number of serum samples in each period. Column IV gives the proportion of samples testing 25OHD ng/mL for the minimum (maximum) week in the half-year period, and column V gives the corresponding mid-week date (month/day). Column VI, , gives the absolute value of the peak-to-trough difference in column IV. Columns VII and VIII give the model prediction and mid-week date of the minimum (maximum) 25OHD proportion, based on model 3 of table 1. Column IX gives the difference in timing between columns V and VIII. The fall/winter 2011–12 model-predicted minimum falls beyond the observed data, so no comparison is made.