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初秋之爽

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[求助] reviewer问题求助。。。。。3sigma rule

有一个关于3sigma rule的问题。。。。请各位大侠帮忙，看看如何回答是好呢？Please provide reference for the 3sigma rule and rational for choosing a cut-off value.

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初秋之爽: 金币+30, ★★★很有帮助 2013-05-26 09:51:07

比如我在我的论文数据作图（Figure 3B，图见http://prl.aps.org/pdf/PRL/v109/i24/e248107）中分划线画在3σ分界线上，审稿人问这条线的确定是遵照什么统计规则，回答就是3σ rule。

Response:
The referee asks whether the divisions of the FACS dot plots are determined by statistical method, which has sufficient numerical confidence. The answer is: YES, they're in accordance with 3σ rule, and the unilateral confidence level is 99.86%; two-dimensional distribution confidence level is 99.72%. Taking Fig. S3 B, C, C-Q1, C-Q2, C-Q1 for example, detailed discussion is below.

Figure R21 Figure 3B, Figure S3B
In our experiments, the FACS instrument’s gain and threshold parameters are adjusted into appropriate values, which make most of the cells’ scatter points in tristable conditions be suitably distributed between upper bound and lower bound. These adjustable instrument parameters are then fixed for all the subsequent experiments. After that, ‘dark’ (both-lowly expressing) cell culture is the reference to determine the divisions of Q1Q2-Q3Q4 and Q1Q3-Q2Q4, as shown in Fig. 3B (Figure R 21). For example, the vertical division between Q1Q3 and Q2Q4 is determined at the position where 99.86% points are on its left, according to 3σ method.

In other words, ‘dark’ state population should be in the left side of this vertical divison with a confidence level 99.86% (confidence coefficient P=0.9986; notice these are all unilateral distributions, while in bilateral case P=0.9973). The same criterion is also applied to the horizontal division. Hence, overall the ‘dark’ state population should be in Q3 region with a confidence level 99.86%*99.86% = 99.72%.

These two divisions are determined for all the following FACS plots (e.g. Fig. S3C, C-Q1, C-Q2, C-Q1, and etc.), to discriminate whether a scatter point is belong to ‘dark’ state with a confidence level 99.72%.