几何平均荧光强度与算术平均荧光强度

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平均荧光强度

通常我们在分析流式结果的时候更多的是去分析细胞群体的比例“%Gated”，还有一个比较重要的一个统计参数是“平均荧光强度”，细胞群体的平均荧光强度分为几何平均荧光强度与算术平均荧光强度，各自都有着比较重要的意义。根据需要我查询了相关的资料，详细的讲解了这两个衡量参数的意义与在分析中起到的作用，供大家参考，若有更好的看法，希望不吝赐教。

Means(平均荧光强度)

The mean is one of the most widely used statistics in flow cytometry.There are two types, the arithmetic and the geometric mean. Both have their uses and are applicable to certain data sets, but choosing to use the wrong one can have a dramatic affect on the results.Let's start with a definition of each type of mean and then move on to some practical examples of the affect the use of each type of mean has on the results we get.

The ARITHMETIC mean.(算术平均荧光强度)

The arithmetic mean is what is normally known as the "average". It is the sum of the individual values of a group divided by the number of values in that group.

Thus (x1 + x2 + x3 ... +xn)/n.

The GEOMETRIC mean.(几何平均荧光强度)

When this is applied to flow cytometry data, what is being done is that over the data range collected, or a subset selected, the channel number is multiplied by the number of counts in that channel number, all the channels get summed, then divided by the total number of counts being considered.

The geometric mean is calculated by multiplying the individual values of a group together and getting the nth root of the product.

Thus (x1 * x2 * x3 ... *xn) nth root.

When this is calculated on flow cytometry data, various software manufacturers approach the calculations in different ways, with some taking into consideration the display resolution, which can affect the result.

By way of an example, if you have a population of five cells, with fluorescence intensities of 1, 100, 100, 100, and 10,000, then their arithmetic mean intensity will calculate to be 2060; their geometric mean will be 100. (Their mode will be 100, and the median value will also be100).

It is the arithmetic mean which gives the cell at 10,000 its "real" weight -- in much the way that one very large kid in the fifth grade can seriously affect the calculated weight of an "average" fifth grader.

The geometric mean sees that the cell at 10,000 is 100 times brighter than the cells at 100; and the cell at 1 is one hundredth as bright as the cells at 100 (i.e. the cells show a log-normal distribution -- they look symmetrical when plotted on log graph paper). Therefore the cell at 10,000 is given equal weight to the cell at 1 in the calculation of the geometric mean