Degree of tumour differentiation (papillary and follicular combined), expressed as % of tumour area, showing the close similarity between the two groups with a short latent period (E1 and E3), and the considerable increase in the % of differentiated tumour in group E2 with a longer latent period. In this and subsequent figures, the box represents the interquartile range. The whiskers are lines that extend from the box to the highest and lowest values, excluding outliers. A line across the box indicates the median. Circles represent outliers (cases between 1.5 and 3 box lengths from the upper or lower end of the box). Stars represent extremes (cases that are beyond 3 box lengths from the upper or lower end of the box).