Statistics IIItcs.inf.kyushu-u.ac.jp/~kijima/GPS20/GPS20-10.pdfStatistics III July 15, 2020...

Statistics III

July 15, 2020

来嶋秀治 (Shuji Kijima)

Dept. Informatics,

Graduate School of ISEE

Todays topics

• interval estimation (区間推定)

• hypothesis testing (仮説検定)

• t-test

• 2-test

確率統計特論 (Probability & Statistics)

Lesson 10

1. Interval estimation

Statistical Inference (統計的推定)

point estimation (点推定)

consistent estimation (一致推定)

unbiased estimation (不偏推定)

maximum likelihood (最尤推定)

interval estimation (区間推定)

Statistical inference3

Example 1

A clerk says “our eggs are big. 70[g] in average.”

You bought 6 eggs in a shop.

How large are eggs sold in this shop?

ത𝑋 = 66.3[g], s2 = 17.584[g2]

Is the clerk honest?

1 2 3 4 5 6

weight[g] 64.3 70.4 63.2 67.8 71.3 60.8

Central Limit Theorem (中心極限定理)4

Def.

A series 𝑌𝑛 w/ distribution functions 𝐹𝑛

converges 𝑌 in distribution (𝑌に分布収束する), if

lim𝑛→∞

𝐹𝑛 = 𝐹 where 𝐹 is the distr. func. of 𝑌.

Thm. Central limit theorem

Suppose 𝑋1, … , 𝑋𝑛 are i.i.d., w/ expectation 𝜇, and variance 𝜎2,

then 𝑍𝑛 ≔1

𝑛σ𝑖=1𝑛 𝑋

𝑖−𝜇

𝜎converges to N(0,1) in distribution.

i.e., lim𝑛→∞

Pr 𝑍𝑛 < 𝑧 = −∞

𝑧 1

2𝜋e−

𝑥2

2 d𝑥

𝑍𝑛 ≔1

𝑛

𝑖=1

𝑛𝑋𝑖 − 𝜇

𝜎=

𝑛

𝜎 𝑛

𝑖=1


𝑛=

1

𝜎𝑛

𝑋 − 𝜇


Example 1


ത𝑋 = 66.3[g], s2 = 17.584[g2] for 6 eggs.

Suppose 2=18.0 for simplicity.

Let z* (>0) satisfy

Pr −𝑧∗ ≤𝑋 − 𝜇𝜎𝑛

≤ 𝑧∗ ≥ 0.95

Since central limit theorem,


≤ 𝑧∗ = න−𝑧∗

𝑧∗ 1

2𝜋𝜎exp −

1

2𝑥2 d𝑥

… and we see that z* = 1.960 (see normal distribution table).

“two-sided 95%

confidence interval”

両側95％信頼区間

Normal distribution6

Wikipedia: Standard normal table

http://en.wikipedia.org/wiki/Normal_distribution

Standard normal table (標準正規分布表)7

Wikipedia: Standard normal table

http://en.wikipedia.org/wiki/Standard_normal_table


Example 1


ത𝑋 = 66.3[g], s2 = 17.584[g2] for 6 eggs.


ത𝑋 = 66.3[g]

𝑧∗ = 1.960

𝜎2 = 18.0

𝑛 = 6


≤ 𝑧∗ =

===

= Pr ?≤ 𝜇 ≤?


Example 1


ത𝑋 = 66.3[g], s2 = 17.584[g2] for 6 eggs.


ത𝑋 = 66.3[g]

𝑧∗ = 1.960

𝜎2 = 18.0

𝑛 = 6


≤ 𝑧∗ = Pr −𝑧∗𝜎

𝑛≤ 𝑋 − 𝜇 ≤ 𝑧∗

𝜎

𝑛

= Pr −𝑋 − 𝑧∗𝜎

𝑛≤ −𝜇 ≤ −𝑋 + 𝑧∗

𝜎

𝑛

= Pr 𝑋 + 𝑧∗𝜎

𝑛≥ 𝜇 ≥ 𝑋 − 𝑧∗

𝜎

𝑛

= Pr 66.3 + 1.96018

6≥ 𝜇 ≥ 66.3 − 1.960

18

6

= Pr 69.69 ≥ 𝜇 ≥ 62.91

2. hypothesis testing (仮説検定)

Todays topics



• t-test

• 2-test

Hypothesis testing (仮説検定)11

Terminology

• null hypothesis (帰無仮説)

• alternative hypothesis (対立仮説)

Idea

Pr[null hypo is true]

reject the null hypothesis with significant level

(有意水準で帰無仮説を棄却する)

Pr[null hypo is true]

fail to reject the null hypothesis with significant level

(有意水準で帰無仮説を棄却しない)


Example 1




ത𝑋 = 66.3[g], s2 = 17.584[g2]


1 2 3 4 5 6

weight[g] 64.3 70.4 63.2 67.8 71.3 60.8


≤ 𝑧∗ =

==

= Pr ?≤ 𝑋 ≤?


Example 1


ത𝑋 = 66.3[g], s2 = 17.584[g2] for 6 eggs.

Let assume = 70.0 Suppose 2=18.0 for simplicity.

𝜇 = 70

𝑧∗ = 1.960

𝜎2 = 18.0

𝑛 = 6

ത𝑋 = 66.3[g]


≤ 𝑧∗ = Pr −𝑧∗𝜎

𝑛≤ 𝑋 − 𝜇 ≤ 𝑧∗

𝜎

𝑛

= Pr 𝜇 − 𝑧∗𝜎

𝑛≤ 𝑋 ≤ 𝜇 + 𝑧∗

𝜎

𝑛

= Pr 70 − 1.96018

6≤ 𝑋 ≤ 70 + 1.960

18

6

= Pr 66.6 ≤ 𝑋 ≤ 73.4


Example 1


ത𝑋 = 66.3[g], s2 = 17.584[g2] for 6 eggs.


It rejects the null hypothesis = 70.0 with significant level 5%

(帰無仮説 = 70.0 は有意水準5%で棄却される．)

𝜇 = 70

𝑧∗ = 1.960

𝜎2 = 18.0

𝑛 = 6

ത𝑋 = 66.3[g]

Exercise15

Example 2

The scores of an examination.

How much ratio do they understand?

student 1 2 3 4 5 6 7 8 9 10

score 72 89 64 52 96 64 70 83 56 70

Q1. Compute the two-sided 95% confidence interval

Q2. Discuss the null hypothesis “the expectation is 80”

with significance level 5%?

𝑋 = 71.6, 𝜎2 ≃ 200 (unbiased variance)

2. t distribution, 2 distribution

Todays topics



• t-test

• 2-test


Example 1




ത𝑋 = 66.3[g], s2 = 17.584[g2]


1 2 3 4 5 6

weight[g] 64.3 70.4 63.2 67.8 71.3 60.8

Student’s t-statistics (スチューデントのt統計量)18

Let assume = 70.0

Let 𝑡: =ത𝑋−𝜇𝑠

𝑛

,

where 𝑠2 ≔σ𝑖=1𝑛 𝑋𝑖− ത𝑋 2

𝑛−1(unbiased estimator of 2).

𝑍𝑛 ≔ത𝑋−𝜇𝜎

𝑛

in Cent. limit. Thm.

Question

Does t follow N(0,1), in a similar way as Z?

Example 1


ത𝑋 = 66.3[g], s2 = 17.584[g2] for 6 eggs.



Question

Does 𝑡 follow N(0,1), in a similar way as 𝑧?

𝑡 =𝜎

𝑠𝑍 =

1

𝑠2

𝜎2

𝑍 =1

1𝜎2

⋅σ𝑖=1𝑛 𝑋𝑖 − 𝑋

2

𝑛 − 1

𝑍 =1

1𝑛 − 1

σ𝑖=1𝑛 𝑋𝑖 − 𝑋

𝜎

2

𝑍

Let 𝑡 =ത𝑋−𝜇𝑠

𝑛

and 𝑍 =ത𝑋−𝜇𝜎

𝑛


𝑛−1(unbiased estimator of 2).

t-distribution and 2distribution20

Prop. 1.

σ𝑖=1𝑛 𝑋𝑖−𝑋

𝜎

2

follows the 𝜒2-distribution with 𝑛 − 1 degrees.

Prop. 2.

𝑋1, … , 𝑋𝑛 ∼ N 0,1 , independently.

Let 𝑌:= 𝑋12 +⋯+ 𝑋𝑛

2, then 𝑌 follows Ga1

2,𝑛

2.

𝜒2-distribution

with 𝑛 degrees

of freedom

𝑡 =𝜎

𝑠𝑍 =

1

𝑠2

𝜎2

𝑍 =1

1𝜎2


2

𝑛 − 1

𝑍 =1

1𝑛 − 1


𝜎

2

𝑍

Idea of Prop. 1 (Not a sketch of proof)21

𝑖=1

𝑛𝑋𝑖 − 𝑋

𝜎

2

=

𝑖=1

𝑛 𝑋𝑖 − 𝜇 − 𝑋 − 𝜇

𝜎

2

=1

𝜎2

𝑖=1

𝑛

𝑋𝑖 − 𝜇 2 − 2 𝑋𝑖 − 𝜇 𝑋 − 𝜇 + 𝑋 − 𝜇2

=

𝑖=1


𝜎

2

− 2 𝑋 − 𝜇σ𝑖=1𝑛 𝑋𝑖 − 𝜇

𝜎2+ 𝑛

𝑋 − 𝜇

𝜎

2

=

𝑖=1


𝜎

2

− 2𝑛𝑋 − 𝜇

𝜎

2

+ 𝑛𝑋 − 𝜇

𝜎

2

=

𝑖=1


𝜎

2

− 𝑛𝑋 − 𝜇

𝜎

2

=

𝑖=1


𝜎

2

−𝑋 − 𝜇𝜎𝑛

2

Rem. if 𝑋 ∼ N 𝜇, 𝜎2 then 𝑋 − 𝜇

𝜎∼ N(0,1)

Rem. if 𝑋 ∼ N 𝜇, 𝜎2 then

𝑋 ∼ N 𝜇,𝜎2

𝑛

t-distribution and 2distribution [William Gosset]22

Prop. 3.

𝑋 ∼ N(0,1), 𝑌 ∼ Ga1

2,𝑛

2, independently.

Then, 𝑋

𝑌

𝑛

follows

𝑓 𝑥 =Γ

𝑛 + 12

𝑛𝜋 Γ𝑛2

1 +𝑥2

𝑛

−𝑛+12

−∞ < 𝑥 < ∞ .

𝑡-distribution

with 𝑛 degrees

of freedom

𝑡 = 𝑍𝜎

𝑠=

𝑍

𝑠2

𝜎2

=𝑍

1𝜎2


2

𝑛 − 1

=𝑍

1𝑛 − 1


𝜎

2

t-distribution and 2distribution [William Gosset]23

𝑡 = 𝑍𝜎

𝑠=

𝑍

𝑠2

𝜎2

=𝑍

1𝜎2


2

𝑛 − 1

=𝑍

1𝑛 − 1


𝜎

2

Thm.

𝑡 follows the 𝑡-distribution with 𝑛 − 1 degrees, i.e.,

𝑓𝑡 𝑥 =Γ

𝑛2

(𝑛 − 1)𝜋 Γ𝑛 − 12

1 +𝑥2

𝑛 − 1

−𝑛2

−∞ < 𝑥 < ∞

Student’s t distribution24

Wikipedia: Student’s t distribution

http://en.wikipedia.org/wiki/Student%27s_t-distribution

2 分布25

Wikipedia: Chi-squared distribution

http://en.wikipedia.org/wiki/Chi-squared_distribution

t-test (t検定)

Todays topics



• t-test

• 2-test

estimation of (expect.)


Example 1




ത𝑋 = 66.3[g], s2 = 17.584[g2]


1 2 3 4 5 6

weight[g] 64.3 70.4 63.2 67.8 71.3 60.8

𝑡-test (𝑡検定)28

𝑡-test

Given samples 𝑋1 = 𝑎1, … , 𝑋𝑛 = 𝑎𝑛.

Q: Does a value 𝑏 estimate E[𝑋]?

Claim

If 1 < 𝛼 it rejects E 𝑋 = 𝑏

If 1 ≥ 𝛼 it fails to reject E 𝑋 = 𝑏

Since 𝑡: =ത𝑋−𝜇𝑠

𝑛

follows t distribution with degree n-1,

Pr null hypo. : E 𝑋 = 𝑏 = Pr 𝑋 − 𝑏 ≥ 𝑎 − 𝑏 ∣ 𝐸 𝑋 = 𝑏

= න−∞

−𝑎−𝑏

𝑠2/𝑛𝑓𝑡 𝑥 𝑑𝑥 + න

𝑎−𝑏

𝑠2/𝑛

∞

𝑓𝑡 𝑥 d𝑥 (1)


Example 1


ത𝑋 = 66.3[g], s2 = 17.584[g2] for 6 eggs.


Let 𝑡: =ത𝑋−𝜇𝑠

𝑛

,


𝑛−1(unbiased estimator of 𝜎2).

Then 𝑡, follows t distribution with degree 𝑛 − 1

𝑓𝑡 𝑥 =Γ

𝑛 + 12

𝑛𝜋 Γ𝑛2

1 +𝑥2

𝑛

−𝑛+12

−∞ < 𝑥 < ∞ .

𝑍𝑛 ≔ത𝑋−𝜇𝜎

𝑛

in Cent. limit. Thm.


Example 1


ത𝑋 = 66.3[g], s2 = 17.584[g2] for 6 eggs.


Let 𝑡∗ (>0) satisfy

Pr −𝑡∗ ≤𝑋 − 𝜇𝑠𝑛

≤ 𝑡∗ = න−𝑡∗

𝑡∗

𝑓𝑡(𝑥)d𝑥 ≥ 0.95

… and we see that 𝑡∗ = 2.571 (see 𝑡-distribution table).


Example 1


ത𝑋 = 66.3[g], s2 = 17.584[g2] for 6 eggs.


ത𝑋 = 66.3[g]

2=17.584

n = 6

z*=2.571

It fails to reject the null hypothesis = 70.0

with significant level 5%

(帰無仮説 = 70.0 は有意水準5%で棄却されない．)

𝑋 − 𝜇

𝑠2

𝑛

=66.3 − 70

17.5846

= 2.161 < 𝑡∗ = 2.571

2-test (2検定)

Todays topics



• t-test

• 2-test

estimation of 2 (variance.)

2-test (2検定)33

2-test

Given samples 𝑋1 = 𝑎1, …𝑋𝑛 = 𝑎𝑛.

Q: Does a value 𝑐2 estimate Var[𝑋]?

Claim

If 2 < 𝛼 it rejects Var 𝑋 = c2

If 2 ≥ 𝛼 it fails to reject Var 𝑋 = c2

Since 𝑆:= σ𝑖=1𝑛 (𝑋𝑖− ത𝑋)2

𝜎2follows

2 distribution with n-1 degrees of freedom,

Pr null hypothesis: Var 𝑋 = 𝑐2 = Pr 𝑆 ≥ 𝑐2 ∣ Var 𝑋 = 𝑐2

= න𝑐2

∞

𝑓𝜒2 𝑥 d𝑥 (2)

2 分布34

Wikipedia: Chi-squared distribution

http://en.wikipedia.org/wiki/Chi-squared_distributionreject

2-test (2検定) Example35

2-test

Suppose the sample variance of weights of 10 balls is 0.35.

Is this smaller than the prescribed value 0.2?

Discuss with significant level 5%

Claim

It fails to reject the null hypothesis with significant level 5%.

(有意水準5%で帰無仮説は棄却されない)

𝑆:=

𝑖=1

𝑛(𝑋𝑖− ത𝑋)2

𝜎2=

𝑛 − 1 𝑠2

𝜎2=

10 − 1 × 0.35

0.2= 15.75 < 16.919

right 5%null hypothesis (帰無仮説)

Var[X] 0.2

2-test (2検定) Example36

2-test

Suppose the sample variance of weights of 100 balls is 0.26.

Is this smaller than the prescribed value 0.2?

Discuss with significant level 5%

𝑆:=

𝑖=1

𝑛(𝑋𝑖− ത𝑋)2

𝜎2=

𝑛 − 1 𝑠2

𝜎2=

100 − 1 × 0.26

0.2= 128.7 > 124.34

null hypothesis (帰無仮説)

Var[X] 0.2

Claim

It rejects the null hypothesis with significant level 5%.

(有意水準5%で帰無仮説は棄却される)

right 5%

Statistical Hypothesis Testing37

z-test: normal distribution

t-test: 𝑡 distribution, such as expectation

2-test: 2 distribution, such as variance

F-test: 𝐹 distribution, such as ratio of variance

Statistics IIItcs.inf.kyushu-u.ac.jp/~kijima/GPS20/GPS20-10.pdfStatistics III July 15, 2020...

Documents

Transcript of Statistics IIItcs.inf.kyushu-u.ac.jp/~kijima/GPS20/GPS20-10.pdfStatistics III July 15, 2020...