关于平均荧光强度的问题

bravegao

最近给人做实验，测血清中抗体浓度，最后分析时遇到问题，拿什么做结果啊，阳性部分？平均荧光强度？这就有问题了，啥是平均荧光强度，是mean、还是GEOmean、还是median,另外，把区内部分偏阳性结果稍稍刨除一点，mean的变化就很大，有时不两个阳性细胞就能造成这样的结果，这平均荧光强度到底有什么意义呢？请专家指教！

niwanmao

这是Purdue中心的专家回答：
The arithmetic mean is the "best" measure of central tendency for true normal (gaussian) distributions, the geometric mean is the same for distributions that are made normal if they are transformed logarithmically (log-normal distribution).
The mean is calculated by summing the values of all measurements and then dividing by the number (n) of measurements, whereas the geometric mean is found by multiplying all measurements and finding the nth root of the product.  The geometric mean sounds hard to calculate, but is what you get if you antilog the arithmetic mean of log data, hence its widespread appearance in flow cytometric analysis programs.  If a  "log" sample is normally distributed (ie Log-normal), then the geometric mean would indicate the centre better than the arithmetic mean.
The median (50th centile) is the value that corresponds to the middle item in a ranked list (ie sorted by magnitude) of all measurements.  It's robust in that it doesn't necessarily move in response to small numbers of outliers, or to skewing of the tails of a distribution, whereas the mean is tugged by both. One situation where the median is probably the only valid measure is where data pile up at one extreme of measurement, as long as more than 50% of the cells are clear of the sides you get a valid median, but either type of mean will be way off.
So if you've got normally distributed data, and want to be able to reflect small changes, use the arithmetic mean, if you've got lognormal data use the geometric mean, and if you want a robust indicator use the median (but this will fail to indicate subtle changes).

jingweis530

很难明白，能否给点实例。

niwanmao

意思就是说：
如果你的数据在线性模式是呈正态分布，那么建议使用平均值（Mean，所有细胞的荧光强度相加，再除以细胞数）。如果数据在Log模式下呈正态分布，那么建议使用几何平均数（GeoMean，所有细胞的荧光强度相乘，再进行N次开方，N＝细胞数）。Median指中位数，是对所有细胞的荧光强度进行排序，位于50％处的荧光强度值。这些统计指标基本上流式分析软件中都能找的到。

jingweis530

明白，谢谢老师指点。

chy

回答的很好

bravegao

豁然开朗，谢谢！

beibei1040

非常有用的答案 解除了分析时的模糊概念

一成天

niwanmao 发表于 2011-2-16 20:24

                               
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意思就是说：
如果你的数据在线性模式是呈正态分布，那么建议使用平均值（Mean，所有细胞的荧光强度相加， ...

荧光抗体做细胞表型分析，FL1 、FL2、FL3等等一般都用的是LOG放大，照倪老师所说，是否可以理解为，当我们求这些荧光信号的MFI 时， 应该用GeoMean来表示？而不是用Mean?
盼复，谢谢！

niwanmao

一成天 发表于 2011-4-11 16:25

                               
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荧光抗体做细胞表型分析，FL1 、FL2、FL3等等一般都用的是LOG放大，照倪老师所说，是否可以理解为，当我 ...

是的。用GEOMEAN最能反映其真实平均水平。