A process for evaluating a set of conditions for staining a population of cells for sorting, the population including a first type and a second type of cell, characterised in that the process includes: (a) staining a fraction of the population of cells with a fluorescent dye under a set of staining conditions; (b) exposing the stained cells to electromagnetic radiation as the stained cells are passed through an interrogation location of a flow cytometer at a rate, R; (c) determining a fluorescence emission characteristic of the exposed cells; (d) using the determined fluorescence characteristic to classify the exposed cells into two or more sub-populations of cells, one of the sub-populations being an enriched sub-population of the first cell type; (e) determining a coefficient of variation for the fluorescence emission characteristic of the cells of the enriched sub-population, wherein a microprocessor provides an automated estimation of the coefficient of variation to provide an indication of sorting efficiency for the staining conditions, wherein the microprocessor provides the automated estimation of the coefficient of variation by estimating 2 nd order statistics of the sub-populations' distributions using a model of known form and finding the best fit of that model to observed data and by using a parametric or non-parametric computer algorithm and wherein the model comprises a four-component model or a three-component model to estimate the characteristics of the subpopulations wherein the subpopulations comprise aligned X sperm cell or aligned Y sperm cell populations; and (f) determining whether to modify any staining condition under which cells are to be stained or the rate, R, at which the stained cells are to be passed through the interrogation location of the flow cytometer in order to improve sorting efficiency (g) applying the modified staining condition to the remainder of the population of cells. (a) staining a fraction of the population of cells with a fluorescent dye under a set of staining conditions; (b) exposing the stained cells to electromagnetic radiation as the stained cells are passed through an interrogation location of a flow cytometer at a rate, R; (c) determining a fluorescence emission characteristic of the exposed cells; (d) using the determined fluorescence characteristic to classify the exposed cells into two or more sub-populations of cells, one of the sub-populations being an enriched sub-population of the first cell type; (e) determining a coefficient of variation for the fluorescence emission characteristic of the cells of the enriched sub-population, wherein a microprocessor provides an automated estimation of the coefficient of variation to provide an indication of sorting efficiency for the staining conditions, wherein the microprocessor provides the automated estimation of the coefficient of variation by estimating 2 nd order statistics of the sub-populations' distributions using a model of known form and finding the best fit of that model to observed data and by using a parametric or non-parametric computer algorithm and wherein the model comprises a four-component model or a three-component model to estimate the characteristics of the subpopulations wherein the subpopulations comprise aligned X sperm cell or aligned Y sperm cell populations; and (f) determining whether to modify any staining condition under which cells are to be stained or the rate, R, at which the stained cells are to be passed through the interrogation location of the flow cytometer in order to improve sorting efficiency (g) applying the modified staining condition to the remainder of the population of cells.