作者chliao2006 (chien)
看板Statistics
標題[問題] variance=0,sample mean=sample median?
時間Wed Apr 22 12:19:36 2015
這是1997年AP Statistics測驗裡的一個問題:
A random sample of size 10 was taken from a population.
The sample has a variance of zero.
Which of the following statements must be true?
1.The population also has a variance of zero.
2.The sample mean is equal to the sample median.
3.The ten data points in the sample are equal in numerical value.
(a) 1 only
(b) 2 only
(c) 3 only
(d) 1 and 2
(e) 2 and 3
答案是:(c)
但是不理解,為何答案不是(e)?
∵The sample has a variance of zero.
∴The ten data points in the sample are equal in numerical value.
那麼不是同時也可得出,The sample mean is equal to the sample median.
請問為何上面這句不正確?
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推 allen1985: 答案錯了? 04/22 12:50
推 expiate: 你查一下median在偶數時該怎麼算應該就會理解了 04/22 13:09
→ expiate: 我好像理解錯了,請忽略我上面的推文,抱歉 04/22 13:13
推 ww770829: 他應該是認為不存在中位數? 04/22 13:30
→ celestialgod: 我也覺得他應該認為沒有中位數,全部一樣 04/22 13:34
推 allen1985: Median always exists? 04/22 15:18
→ BugEater: 我選e 04/22 16:04
→ celestialgod: 所以是E 04/22 17:04
推 goshfju: 原po是對的 04/23 00:11
推 goshfju: 1. 顯然是錯的 隨便找都有反例 04/23 00:13
推 goshfju: 樣本變異數0就代表樣本10個數字都ㄧ樣(3對)而樣本平均 04/23 00:15
→ goshfju: 數跟樣本中位數也是那個數字(2對) 04/23 00:15
→ chliao2006: 多謝大家的回答,幫助考量到關於存在的問題。 04/23 02:18