正态分布图--直方图的关系
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Z
Hale Waihona Puke Baidu
X μx X μx σx σ/ n
Standard Normal Distribution
σ5
Normal Distribution
-2
0
X μ x 10 Z σ 5
In symmetrical data sets, where the mean and median are the same ,you can use the empirical rule to examine the variability.
（1-1/k2）*100% • Consider k=2, the result of the formula is 75%, that states that at least 75% of the values must be found within ±2 standard deviations of the mean.
p
Z
X μ σ
68%
95%
-3 -2 -1 0 1 2 3 z
99.7%
Z 0.00 0.01 0.02 …
. 2.0 0.1
. 0.0 .
.9772
p
The chebyshev rule切比雪夫
• The chebyshev rule states that for any data set, regardless of shape, the percentage of values that are found within distances of k standard deviations from the mean must be at least:
1
6
8
12
14 18 20 22
7 6 Frequency 5 4 3 2 1 0 0 5 10
15
20
25
1
6
8
12
14 18 20 22
7
6 Frequency 5 4 3 2 1 0 0 5 10 15 20 25
Got the mean of each two values
x
1 6 8 12 231 14 18 20 22