Correction of modal DNA values obtained by microspectrophotometry and tests for their shifts

The technical problems in the application of statistical analyses of the nuclear DNA contents measured by plug or two-wavelength Feulgen microspectrophotometry were discussed. The skewness of the nuclear DNA content unimodally distributed in a cluster could be corrected by logarithmic transformation. A mean value of the logarithmically transformed DNA contents was a more logical characterization of cancer than a graphically obtained mode of nontransformed values. Equations were derived to estimate the number of cells in the G1- and S-phases of mitotic cycles contained within the cluster and to estimate the correction factor of the mean of transformed values of cells in the G1-phase. Thus statistical tests for a shift in the nuclear DNA content of the cells in question in the G1-phase from that of control cells were made possible.