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sabrinayue · 2022年03月19日

求分位点分母为什么是n-1

  1. FRM I
  2. Quantitative

NO.PZ2020010304000036

问题如下：

For the following data:

a. What is the median?

b. What is the IQR?

解释：

a. The first step is to rank order the observations.

From here, we anchor the first observation at 0% and the last at 100%, equally spacing the in-between val-ues. The divisions here will be 100/n-1 = 20%:

The median (50%) lies exactly half way between the third and fourth ranked observations. Therefore:

Median=(0.28+0.38)/2=0.33

b. This requires calculating the 25% and 75% levels.

The 25% level is 5/20 = 25% of the way between ranked observations 2 and 3. Therefore: q25% = 0.75 * 0.27 + 0.25 * 0.28 = 0.2725

Similarly, the 75% level is 75% of the way between observations 4 and 5: q75% = 0.25 * 0.38 + 0.75 * 0.43 = 0.4175

Thus, IQR = (0.2725, 0.4175).

求分位点分母为什么是n-1？

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1 个答案

李坏_品职助教 · 2022年03月19日

嗨，努力学习的PZer你好：


这道题一共有6个观察数据，按照从0到100%这样排列，所以第1个数据是0%，第二个数据是20%，第三个数据是40%……第6个数据是100%分位点。


所以25%的分位数是在第2个位置和第3个位置之间进行选择。


设25%分位数为x，按照线性插值法计算:


（25%-20%）/ (x-0.27) = (40%-20%)/(0.28-0.27) 计算可得，x=0.2725

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NO.PZ2020010304000036问题如下For the following ta:Whis the mean? Whis the IQR?The first step is to rank orr the observations.From here, we anchor the first observation 0% anthe last 100%, equally spacing the in-between val-ues. The visions here will 100/n-1 = 20%:The me(50%) lies exactly half wbetween the thiranfourth rankeobservations. Therefore:Mean=(0.28+0.38)/2=0.33 This requires calculating the 25% an75% levels.The 25% level is 5/20 = 25% of the wbetween rankeobservations 2 an3. Therefore: q25% = 0.75 * 0.27 + 0.25 * 0.28 = 0.2725Similarly, the 75% level is 75% of the wbetween observations 4 an5: q75% = 0.25 * 0.38 + 0.75 * 0.43 = 0.4175Thus, IQR = (0.2725, 0.4175). 老师，这种方式也叫插分吗？

2024-05-13 16:04 1 · 回答

NO.PZ2020010304000036 问题如下 For the following ta:Whis the mean? Whis the IQR? The first step is to rank orr the observations.From here, we anchor the first observation 0% anthe last 100%, equally spacing the in-between val-ues. The visions here will 100/n-1 = 20%:The me(50%) lies exactly half wbetween the thiranfourth rankeobservations. Therefore:Mean=(0.28+0.38)/2=0.33 This requires calculating the 25% an75% levels.The 25% level is 5/20 = 25% of the wbetween rankeobservations 2 an3. Therefore: q25% = 0.75 * 0.27 + 0.25 * 0.28 = 0.2725Similarly, the 75% level is 75% of the wbetween observations 4 an5: q75% = 0.25 * 0.38 + 0.75 * 0.43 = 0.4175Thus, IQR = (0.2725, 0.4175). 应该怎么求？没看懂解析。

2024-02-03 15:28 2 · 回答

NO.PZ2020010304000036正常情况下不是默认取这6个数的概率相同吗，那每个数应该是100%/6，我认为第一个数应该是有概率的

2022-06-23 13:57 1 · 回答

NO.PZ2020010304000036 做题思路都是默认第一个数的概率是0%，然后其余的数平分100%的概率，并按照从小到大和累计概率来排序，是这样吗？ 假如这道题是11个数，那么升序排列后概率依次为0%、10%······100%， （假如还是这些数）四分之一分位点就是q25%=0.27*50%+0.28*50%=0.275； 或者用线性差值法来做（x-0.27）/（0.28-0.27）=（25%-20%）/（30%-20%） 辛苦老师解答！

2022-02-18 18:05 1 · 回答