There are many ways to analyze a histogram. Some very simple methods are often satisfactory to obtain the required information. For example, there might be an interest in identifying positive from negative expressing cells. If there is a significant difference in the fluorescence distributions, a simple positive gate will give you the answer you need. If however, there is overlap between the populations a more sophisticated approach might be needed. This is the area where significant caution must be taken as analysis now becomes more complex. Comparison between histograms requires considerable care. Statistical methods must be used to determine significant difference between populations. The coefficient of variation (CV) is an important measure of the variation that exists between cells within a population. Other statistical components will be introduced.