Statistics- Tests of Hypotheses

8/3/2019 Statistics- Tests of Hypotheses

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1

Tests of Hypotheses:

Small SamplesChapter

Rejection

region


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2CHAPTER GOALS

TO DESCRIBE THE MAJORCHARACTERISTICS OF STUDENTS

t-DISTRIBUTION.

TO UNDERSTAND THE DIFFERENCE

BETWEEN THE t-DISTRIBUTION AND

THEz-DISTRIBUTION.


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3CHAPTER GOALS

TO TEST A HYPOTHESIS INVOLVING ONEPOPULATION MEAN.

TO TEST A HYPOTHESIS INVOLVING THE

DIFFERENCE BETWEEN TWO

POPULATION MEANS.

TO CONDUCT A TEST OF HYPOTHESIS

FORTHE DIFFERENCE BETWEEN A SET

OF PAIRED OBSERVATIONS.


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4

The t-distribution has the following properties: Itiscontinuous, bellshapedandsymmetrical

about zerolikethez-distribution.

Thereisa familyoft-distributions withmeanofzero butone foreachsamplesize.

Thet-distributionismorespreadoutand flatter

atthecenterthanthez-

distribution, butapproachesthez-distributionas

thesamplesizegetslarger.

CHARACTERISTICS OF STUDENTS

t-DISTRIBUTION


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5

z-distribution

t-distribution

Thedegreesof

freedom for

thet-distribution

is df = n - 1.


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6A TEST FOR A POPULATION MEAN:SMALL SAMPLE, POPULATION

STANDARD DEVIATION UNKNOWN

Theteststatistic foraonesamplecaseisgiven

byequation(9-1) below

(9-1) t

X

nS!

Q

/


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7 Thecurrentrate forproducing 5 amp fusesat

Monarch Electric Companyis 250 perhour. A

new machinehas beenpurchasedandinstalled

that,accordingtothesupplier, willincreasethe

productionrate. A sampleof 10 randomlyselectedhours fromlastmonthrevealedthe

meanhourlyproductiononthenew machine

was 256, withasamplestandarddeviationof 6

perhour. Atthe 0.05 significancelevelcan

Monarchconcludethatthenew machineis

faster?

EXAMPLE 1


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8EXAMPLE 1 (continued)

Step 1: Statethenullandthealternative

hypotheses.

H0:Q e 250 H1:Q" 250

Step 2: Statethedecisionrule.

H0 is rejected if t> 1.833,df = 9(Appendix F).

Step 3: Computethevalueoftheteststatistic.

t=

[256-

250]/[6/

10]=

3.16.Step 4: Whatisthedecisionon H0?

H0 isrejected. Thenew machineis faster.


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9STUDENT tDISTRIBUTION

Level of significance for one-tailed test

df .10 .05 .025 .01 .005 .0005

Level of significance for two-tailed test

.20 .10 .05 .02 .01 .0011 3.078 6.314 12.706 31.821 63.657 636.6192 1 .886 2.920 4.303 6.965 9.925 31 .5993 1.638 2.353 3.182 4.541 5.841 12.924

4 1.533 2.132 2.776 3.747 4.604 8.610

5 1.476 2.015 2.571 3.365 4.032 6.869

6 1.440 1.943 2.447 3.143 3.707 5.959

7 1.415 1.895 2.365 2.998 3.499 5.408

8 1.397 1.860 2.306 2.896 3.355 5.041

9 1.383 1.833 2.262 2.821 3.250 4.781

10 1.372 1.812 2.228 2.764 3.169 4.587

11 1.363 1.796 2.201 2.718 3.106 4.437

12 1.356 1.782 2.179 2.681 3.055 4.318

13 1.350 1.771 2.160 2.650 3.012 4.221

14 1.345 1.761 2.145 2.624 2.977 4.140

15 1.341 1.753 2.131 2.602 2.947 4.073

16 1.337 1.746 2.120 2.583 2.921 4.015

17 1.333 1.740 2.110 2.567 2.898 3.965

18 1.330 1.734 2.101 2.552 2.878 3.922

19 1.328 1.729 2.093 2.539 2.861 3.883

20 1.325 1.725 2.086 2.528 2.845 3.850

21 1.323 1.721 2.080 2.518 2.831 3.819

22 1.321 1.717 2.074 2.508 2.819 3.792

23 1.319 1.714 2.069 2.500 2.807 3.768

24 1.318 1.711 2.064 2.492 2.797 3.745

25 1.316 1.708 2.060 2.485 2.787 3.725

26 1.315 1.706 2.056 2.479 2.779 3.707

27 1.314 1.703 2.052 2.473 2.771 3.690

28 1.313 1.701 2.048 2.467 2.763 3.674

29 1.311 1.699 2.045 2.462 2.756 3.659

30 1.310 1.697 2.042 2.457 2.750 3.646

40 1.303 1.684 2.021 2.423 2.704 3.551

60 1 .296 1 .671 2.000 2.390 2.660 3.460

120 1.289 1.658 1.980 2.358 2.617 3.373

1 .282 1 .645 1 .960 2.326 2.576 3.291


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10Display of the Rejection Region, CriticalValue, and the computed Test Statistic

Regionof

rejection

t

Critical

value

1.833

0.05

df= 9


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11

Toconductthistest,threeassumptionsarerequired:

1. Thepopulationsmust benormallyor

approximatelynormallydistributed.2. Thepopulationsmust beindependent.

3. Thepopulationvariancesmust beequal.

Letsubscript 1 and 2 beassociated withpopulation 1 and 2 respectively.

COMPARING TWO POPULATIONS

MEANS


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12POOLED SAMPLE VARIANCE AND

TEST STATISTIC

Pooled Sample Variance

sn s n s

n n

Test Statistic

t X X

s n n

p

p

=

1

2 1 12

2 22

1 2

2

2

1 2

1 1

2

1 1

!

( ) ( )

(9 -3)

(9 -2)


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13EXAMPLE 2A recent Environmental Protection Agency

(EPA) studycomparedthehighway fuel

economyofdomesticandimportedpassengers

cars. A sampleof 15 domesticcarsrevealeda

meanof 33.7 mpg withastandarddeviationof2.4 mpg. A sampleof 12 importedcarsrevealed

ameanof 35.7 mpg withastandarddeviationof

3.9. Atthe 0.05 significancelevelcanthe EPA

concludethatthemilespergallonishigheron

theimportedcars? (Let subscript 1 be associated

with the domestic cars).


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14

Step 1: Statethenullandthealternative

hypotheses.

H0:Q e Q H1:Q " Q

Step 2: Statethedecisionrule.

H0 is rejected if t> 1.708,df= 25.

Step 3: Computethevalueoftheteststatistic.

t= 1.64 (Verify).

Step 4: Whatisthedecisionon H0?

H0 isnotrejected. Insufficientsampleevidence

toclaimahighermpgontheimportedcars.

EXAMPLE 2 (continued)


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df .10 .05 .025 .01 .005 .0005


.20 .10 .05 .02 .01 .0011 3.078 6.314 12.706 31.821 63.657 636.6192 1 .886 2.920 4.303 6.965 9.925 31 .5993 1.638 2.353 3.182 4.541 5.841 12.924

4 1.533 2.132 2.776 3.747 4.604 8.610

5 1.476 2.015 2.571 3.365 4.032 6.869

6 1.440 1.943 2.447 3.143 3.707 5.959

7 1.415 1.895 2.365 2.998 3.499 5.408

8 1.397 1.860 2.306 2.896 3.355 5.041

9 1.383 1.833 2.262 2.821 3.250 4.781

10 1.372 1.812 2.228 2.764 3.169 4.587

11 1.363 1.796 2.201 2.718 3.106 4.437

12 1.356 1.782 2.179 2.681 3.055 4.318

13 1.350 1.771 2.160 2.650 3.012 4.221

14 1.345 1.761 2.145 2.624 2.977 4.140

15 1.341 1.753 2.131 2.602 2.947 4.073

16 1.337 1.746 2.120 2.583 2.921 4.015

17 1.333 1.740 2.110 2.567 2.898 3.965

18 1.330 1.734 2.101 2.552 2.878 3.922

19 1.328 1.729 2.093 2.539 2.861 3.883

20 1.325 1.725 2.086 2.528 2.845 3.850

21 1.323 1.721 2.080 2.518 2.831 3.819

22 1.321 1.717 2.074 2.508 2.819 3.792

23 1.319 1.714 2.069 2.500 2.807 3.768

24 1.318 1.711 2.064 2.492 2.797 3.745

25 1.316 1.708 2.060 2.485 2.787 3.725

26 1.315 1.706 2.056 2.479 2.779 3.707

27 1.314 1.703 2.052 2.473 2.771 3.690

28 1.313 1.701 2.048 2.467 2.763 3.674

29 1.311 1.699 2.045 2.462 2.756 3.659

30 1.310 1.697 2.042 2.457 2.750 3.646

40 1.303 1.684 2.021 2.423 2.704 3.551

60 1 .296 1 .671 2.000 2.390 2.660 3.460

120 1.289 1.658 1.980 2.358 2.617 3.373

1 .282 1 .645 1 .960 2.326 2.576 3.291


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16Sampling Distribution for the Statistic t for aTwo-Tailed Test, 0.05 Level of Significance

Critical

value

2.06

Critical

value

-2.06

0.95

Donotreject H0

Regionof

rejection

Regionof

rejection

0.025 0.025

t-2.06 2.06

df= 25

0


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17

Usethe followingtest whenthesamplesaredependent.

Forexample,supposeyou werecollectingdata

onthepricecharged bytwodifferent bodyshops

becauseyoususpectthatoneischargingmore

thantheother.

Inthiscase,thesame wreckedvehicle will be

assessed bythetwoshops.

Becauseofthis,thesamples will bedependent.

Here we willtakethedifferenceofthetwo

estimatesandperformatestonthedifferences.

HYPOTHESIS TESTING INVOLVING

PAIRED OBSERVATIONS


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18TEST STATISTIC

(9 - 4)

d-baristheaverageofthedifferences

sdisthestandarddeviationofthedifferences

n isthenumberofpairs (differences)

td

s nd

!/


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19Anindependenttestingagencyiscomparingthe

dailyrentalcost forrentingacompactcar from

Hertz and Avis. A randomsampleofeightcities

isobtainedandthe followingrentalinformation

obtained. Atthe 0.05 significancelevelcanthetestingagencyconcludethatthereisadifference

intherentalcharged?

NO

TE: Thesesamplesaredependentsincethesametypeofcar (compact) is beingrented from

thetwocompaniesinthesamecities.

EXAMPLE 3


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20EXAMPLE 3 (continued)


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21 Statethenullandthealternativehypotheses:

H0:Qd = H1:Qd {

Statethedecisionrule.

H0 is

rejected

if

t 2.365.

Computethevalueoftheteststatistic.

t= (1.00)/[3.162/] = 0.89, (verify).

Whatisthedecisiononthenullhypothesis?H0 isnotrejected. Thereisnodifferenceinthe

charge.

EXAMPLE 3 (continued)


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df .10 .05 .025 .01 .005 .0005


.20 .10 .05 .02 .01 .001

1 3.078 6.314 12.706 31.821 63.657 636.6192 1 .886 2.920 4.303 6.965 9.925 31 .5993 1.638 2.353 3.182 4.541 5.841 12.924

4 1.533 2.132 2.776 3.747 4.604 8.610

5 1.476 2.015 2.571 3.365 4.032 6.869

6 1.440 1.943 2.447 3.143 3.707 5.959

7 1.415 1.895 2.365 2.998 3.499 5.408

8 1.397 1.860 2.306 2.896 3.355 5.041

9 1.383 1.833 2.262 2.821 3.250 4.781

10 1.372 1.812 2.228 2.764 3.169 4.587

11 1.363 1.796 2.201 2.718 3.106 4.437

12 1.356 1.782 2.179 2.681 3.055 4.318

13 1.350 1.771 2.160 2.650 3.012 4.221

14 1.345 1.761 2.145 2.624 2.977 4.140

15 1.341 1.753 2.131 2.602 2.947 4.073

16 1.337 1.746 2.120 2.583 2.921 4.015

17 1.333 1.740 2.110 2.567 2.898 3.965

18 1.330 1.734 2.101 2.552 2.878 3.922

19 1.328 1.729 2.093 2.539 2.861 3.883

20 1.325 1.725 2.086 2.528 2.845 3.850

21 1.323 1.721 2.080 2.518 2.831 3.819

22 1.321 1.717 2.074 2.508 2.819 3.792

23 1.319 1.714 2.069 2.500 2.807 3.768

24 1.318 1.711 2.064 2.492 2.797 3.745

25 1.316 1.708 2.060 2.485 2.787 3.725

26 1.315 1.706 2.056 2.479 2.779 3.707

27 1.314 1.703 2.052 2.473 2.771 3.690

28 1.313 1.701 2.048 2.467 2.763 3.674

29 1.311 1.699 2.045 2.462 2.756 3.659

30 1.310 1.697 2.042 2.457 2.750 3.646

40 1.303 1.684 2.021 2.423 2.704 3.551

60 1 .296 1 .671 2.000 2.390 2.660 3.460

120 1.289 1.658 1.980 2.358 2.617 3.373

1 .282 1 .645 1 .960 2.326 2.576 3.291


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23

2.3650

Computed

t=0.89

Rejection

region

-2.365

Rejection

region

0.89

df=

7

t


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24

Chapter 11 : CD-ROM

Chapter 12 : CD-ROM

Chapter 13 : CD-ROM

Homework for Chapter 11,12,13

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Statistics- Tests of Hypotheses

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