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Churning · 2019年10月31日

问一道题:NO.PZ2017092702000150

问题如下:

Based on the table below, which of the following statements is correct?

A

2B

7C

15D

2

选项:

A.

The relative frequency of Interval C is 15.

B.

The cumulative frequency of Interval D is 100%.

C.

The cumulative relative frequency of Interval C is 92.3%.

解释:

C is correct because the cumulative relative frequency of an interval tells us the fraction of all observations that are less than the upper limit of an interval. For Interval C, that would be (2 + 7 + 15)/26 = 92.3%.
A is incorrect because the relative frequency of an interval is the absolute frequency of that interval divided by the total number of observations, here 15/26 = 57.7%. The number 15 represents Interval C’s absolute frequency (also known as frequency), which is simply the actual number of observations in a given interval.
B is incorrect because the cumulative frequency tells us the number of observations that are less than the upper limit of a return interval, not the percentage of observations meeting that criteria. Because Interval D is the uppermost return interval, its cumulative frequency is the total number of observations for all intervals, yielding 2 + 7 + 15 + 2 = 26 and not 100%, which is the cumulative relative frequency for Interval D.


老师问下b为什么错呢 答案里的解释还是没有很理解

1 个答案
已采纳答案

星星_品职助教 · 2019年10月31日

同学你好,

这道题需要区分两个概念。B选项中的cumulative frequency,指得是cumulative (absolute) frequency。这个概念指得是一个数字,而并非一个百分比。所以对于D区间而言,cumulative frequency是26,而非100%。

作为对比,C选项明确说明了问的是cumulative RELATIVE frequency,所以就是一个百分比的形式,计算出来是92.3%。

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