COMPUTING THE CENTRAL LOCATION OF IMMUNOFLUORESCENCE DISTRIBUTIONS - LOGARITHMIC DATA TRANSFORMATIONS ARE NOT ALWAYS APPROPRIATE

The idea of the ''average'' intensity of immunofluorescence data is of ten poorly defined, with such terms as average, mean, and peak used in terchangeably. In addition, the common use of logarithmic amplifiers w ith immunofluorescence data further complicates the problem. Log ampli fiers permit the display of a wider range of fluorescence intensities. At the same time, they effect a log transformation of the data. This transformation decreases the variance resulting in narrower fluorescen ce distributions, which are assumed to approximate normal distribution s. When the log transform is used, the distribution mean is the geomet ric mean of the untransformed data, which is computed simply as the me an of the channel values. This mean value serves as a simple indicator of the population center. Despite the prevalence of log transformatio ns in flow cytometry, this transformation may not yield normally distr ibuted immunofluorescence data, whereas the square root or other fract ional power transformations can yield normal distributions. (C) 1994 W iley-Liss, Inc.