The 'normal range' and precision of phytohaemagglutinin-induced equine lymphocyte transformation in vitro

Data are presented on lymphocyte transformation by phytohaemagglutinin in 20 normal horses. The logarithms of transformation ratios were found to have an approximately normal distribution, giving (for the transformation ratios themselves) a geometric mean of 23.6, a range of 1.92 to 97.3, and an estimated 95 per cent tolerance interval of 1.1 to 488. Analysis of variance on the logarithms of the transformation ratios gave a coefficient of variation of 140 per cent of the transformation ratios themselves for the variation between horses; whereas the coefficient of variation between duplicate samples was only 20 per cent, that is, small compared to the variation between horses. In addition, wide fluctuations of response of individual horses over weekly periods of measurement (comparable with the variation between the horses themselves) suggest that a single set of measurements at one time cannot be taken as evidence of abnormality in a given horse.