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Chapter 9Chapter 9 Hypothesis Testing Hypothesis Testing
Developing Null and Alternative HypothesesDeveloping Null and Alternative Hypotheses Type I and Type II ErrorsType I and Type II Errors Population Mean: Population Mean: Known Known Population Mean: Population Mean: Unknown Unknown
Population ProportionPopulation Proportion
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Developing Null and Alternative Developing Null and Alternative HypothesesHypotheses
Hypothesis testingHypothesis testing can be used to determine whether can be used to determine whether a statement about the value of a population parametera statement about the value of a population parameter should or should not be rejected.should or should not be rejected. The The null hypothesisnull hypothesis, , denoted by denoted by HH0 0 , , is a tentativeis a tentative assumption about a population parameter.assumption about a population parameter. The The alternative hypothesisalternative hypothesis, denoted by , denoted by HHaa, is the, is the
opposite of what is stated in the null hypothesis.opposite of what is stated in the null hypothesis. The alternative hypothesis is what the test isThe alternative hypothesis is what the test is attempting to establish.attempting to establish.
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Testing Research HypothesesTesting Research Hypotheses
Developing Null and Alternative Developing Null and Alternative HypothesesHypotheses
• The The research hypothesisresearch hypothesis should be expressed as should be expressed as the the alternative hypothesisalternative hypothesis..
• The conclusion that the research hypothesis is trueThe conclusion that the research hypothesis is true comes from sample data that contradict the nullcomes from sample data that contradict the null hypothesis.hypothesis.
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Developing Null and Alternative Developing Null and Alternative HypothesesHypotheses
Testing the Validity of a ClaimTesting the Validity of a Claim
• Manufacturers’ claimsManufacturers’ claims are usually given the benefit are usually given the benefit of the doubt and stated of the doubt and stated as the null hypothesisas the null hypothesis..
• The conclusion that the claim is false comes fromThe conclusion that the claim is false comes from sample data that contradict the null hypothesis.sample data that contradict the null hypothesis.
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One-tailedOne-tailed(lower-tail)(lower-tail)
One-tailedOne-tailed(upper-tail)(upper-tail)
Two-tailedTwo-tailed
0 0: H 0 0: H
0: aH 0: aH 0 0: H 0 0: H
0: aH 0: aH 0 0: H 0 0: H
0: aH 0: aH
Summary of Forms for Null and Summary of Forms for Null and Alternative Hypotheses about a Alternative Hypotheses about a
Population MeanPopulation Mean The The equality partequality part of the hypotheses always appears of the hypotheses always appears
in the in the null hypothesisnull hypothesis.. In general, a hypothesis test about the value of aIn general, a hypothesis test about the value of a population mean population mean must take one of the followingmust take one of the following three forms (where three forms (where 00 is the hypothesized value of is the hypothesized value of the population mean).the population mean).
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The director of medical servicesThe director of medical serviceswants to formulate a hypothesiswants to formulate a hypothesistest that could use a sample oftest that could use a sample ofemergency response times toemergency response times todetermine whether or not thedetermine whether or not theservice goal of 12 minutes or lessservice goal of 12 minutes or lessis being achieved.is being achieved.
Example: Metro EMSExample: Metro EMS
Null and Alternative HypothesesNull and Alternative Hypotheses
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Null and Alternative HypothesesNull and Alternative Hypotheses
The emergency service is meetingThe emergency service is meeting
the response goal; no follow-upthe response goal; no follow-up
action is necessary.action is necessary.
The emergency service is notThe emergency service is not
meeting the response goal;meeting the response goal;
appropriate follow-up action isappropriate follow-up action is
necessary.necessary.
HH00: :
HHaa::
where: where: = mean response time for the population = mean response time for the population of medical emergency requestsof medical emergency requests
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Type I ErrorType I Error
Because hypothesis tests are based on sample data,Because hypothesis tests are based on sample data, we must allow for the possibility of errors.we must allow for the possibility of errors. A A Type I errorType I error is rejecting is rejecting HH00 when it is true. when it is true.
The probability of making a Type I error when theThe probability of making a Type I error when the
null hypothesis is true as an equality is called thenull hypothesis is true as an equality is called the
level of significancelevel of significance..
Applications of hypothesis testing that only controlApplications of hypothesis testing that only control
the Type I error are often called the Type I error are often called significance testssignificance tests..
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Type II ErrorType II Error
A A Type II errorType II error is accepting is accepting HH00 when it is false. when it is false.
It is difficult to control for the probability of makingIt is difficult to control for the probability of making
a Type II error.a Type II error.
Statisticians avoid the risk of making a Type IIStatisticians avoid the risk of making a Type II
error by using “do not reject error by using “do not reject HH00” and not “accept ” and not “accept HH00”.”.
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Type I and Type II ErrorsType I and Type II Errors
CorrectCorrectDecisionDecision Type II ErrorType II Error
CorrectCorrectDecisionDecisionType I ErrorType I Error
RejectReject HH00
(Conclude (Conclude > 12) > 12)
AcceptAccept HH00
(Conclude(Conclude << 12) 12)
HH0 0 TrueTrue(( << 12) 12)
HH0 0 FalseFalse
(( > 12) > 12)ConclusionConclusion
Population Condition Population Condition
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Test StatisticTest Statistic
Tests About a Population Mean:Tests About a Population Mean: Known Known
nxz/
0
n
xz/
0
This test statistic follows the This test statistic follows the standard normal distribution.standard normal distribution.
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pp-Value Approach to-Value Approach toOne-Tailed Hypothesis TestingOne-Tailed Hypothesis Testing
Reject Reject HH00 if the if the pp-value -value << ..
The The pp-value-value is the probability, computed using the is the probability, computed using the test statistic, that test statistic, that measures the support (or lack ofmeasures the support (or lack of support) provided by the sample for the nullsupport) provided by the sample for the null hypothesishypothesis..
If the If the pp-value is less than or equal to the level of-value is less than or equal to the level of significance significance , the value of the test statistic is in the, the value of the test statistic is in the rejection region.rejection region.
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pp-Value Approach-Value Approach pp-Value Approach-Value Approach
p-valuep-value
00 -z = -1.28 -z = -1.28
= .10 = .10
zz
z =-1.46 z =-1.46
Lower-Tailed Test About a Population Lower-Tailed Test About a Population Mean:Mean:
KnownKnown
Samplingdistribution
of
Samplingdistribution
of z xn
0
/z x
n
0
/
pp-Value -Value << ,,
so reject so reject HH00..
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pp-Value Approach-Value Approach pp-Value Approach-Value Approach
p-Valuep-Value
00 z = 1.75 z = 1.75
= .04 = .04
zz
z =2.29 z =2.29
Upper-Tailed Test About a Population Upper-Tailed Test About a Population Mean:Mean:
KnownKnown
Samplingdistribution
of
Samplingdistribution
of z xn
0
/z x
n
0
/
pp-Value -Value << ,,so reject so reject HH00..
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Critical Value Approach to Critical Value Approach to One-Tailed Hypothesis TestingOne-Tailed Hypothesis Testing
The test statistic The test statistic zz has a standard normal probability has a standard normal probability distribution.distribution.
We can use the standard normal probabilityWe can use the standard normal probability distribution table to find the distribution table to find the zz-value with an -value with an areaarea of of in the lower (or upper) tail of the in the lower (or upper) tail of the distribution.distribution.
The value of the test statistic that established theThe value of the test statistic that established the boundary of the rejection region is called theboundary of the rejection region is called the critical valuecritical value for the test. for the test.
The rejection rule is:The rejection rule is:• Lower tail: Reject Lower tail: Reject HH00 if if zz << - -zz
• Upper tail: Reject Upper tail: Reject HH00 if if zz >> zz
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00 z = 1.28 z = 1.28
Reject H0Reject H0
Do Not Reject H0Do Not Reject H0
zz
Samplingdistribution
of
Samplingdistribution
of z xn
0
/z x
n
0
/
Lower-Tailed Test About a Population Lower-Tailed Test About a Population Mean:Mean:
KnownKnown Critical Value ApproachCritical Value Approach Critical Value ApproachCritical Value Approach
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00 z = 1.645 z = 1.645
Reject H0Reject H0
Do Not Reject H0Do Not Reject H0
zz
Samplingdistribution
of
Samplingdistribution
of z xn
0
/z x
n
0
/
Upper-Tailed Test About a Population Upper-Tailed Test About a Population Mean:Mean:
KnownKnown Critical Value ApproachCritical Value Approach Critical Value ApproachCritical Value Approach
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Steps of Hypothesis TestingSteps of Hypothesis Testing
Step 1.Step 1. Develop the null and alternative hypotheses. Develop the null and alternative hypotheses.
Step 2.Step 2. Specify the level of significance Specify the level of significance ..
Step 3.Step 3. Collect the sample data and compute Collect the sample data and compute the test statistic.the test statistic.
pp-Value Approach-Value Approach
Step 4.Step 4. Use the value of the test statistic to compute the Use the value of the test statistic to compute the pp-value.-value.
Step 5.Step 5. Reject Reject HH00 if if pp-value -value << ..
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Critical Value ApproachCritical Value Approach
Step 4.Step 4. Use the level of significance Use the level of significanceto to determine the critical value and the determine the critical value and the rejection rule.rejection rule.
Step 5.Step 5. Use the value of the test statistic and the Use the value of the test statistic and the rejectionrejection
rule to determine whether to reject rule to determine whether to reject HH00..
Steps of Hypothesis TestingSteps of Hypothesis Testing
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Example: Metro EMSExample: Metro EMS
The EMS director wants toThe EMS director wants toperform a hypothesis test, with aperform a hypothesis test, with a.05 level of significance, to determine.05 level of significance, to determinewhether the service goal of 12 minutes or less is beingwhether the service goal of 12 minutes or less is beingachieved.achieved.
The response times for a randomThe response times for a randomsample of 40 medical emergenciessample of 40 medical emergencieswere tabulated. The sample meanwere tabulated. The sample meanis 13.25 minutes. The populationis 13.25 minutes. The populationstandard deviation is believed tostandard deviation is believed tobe 3.2 minutes.be 3.2 minutes.
One-Tailed Tests About a Population One-Tailed Tests About a Population Mean:Mean:
KnownKnown
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1. Develop the hypotheses.1. Develop the hypotheses.
2. Specify the level of significance.2. Specify the level of significance. = .05= .05
HH00: :
HHaa::
pp -Value and Critical Value Approaches -Value and Critical Value Approaches
One-Tailed Tests About a Population One-Tailed Tests About a Population Mean:Mean:
KnownKnown
3. Compute the value of the test statistic.3. Compute the value of the test statistic.
13.25 12 2.47
/ 3.2/ 40x
zn
13.25 12 2.47
/ 3.2/ 40x
zn
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5. Determine whether to reject 5. Determine whether to reject HH00..
pp –Value Approach –Value Approach
One-Tailed Tests About a Population One-Tailed Tests About a Population Mean:Mean:
KnownKnown
4. Compute the 4. Compute the pp –value. –value.
For For zz = 2.47, cumulative probability = .9932. = 2.47, cumulative probability = .9932.
pp–value = 1 –value = 1 .9932 = .0068 .9932 = .0068
Because Because pp–value = .0068 –value = .0068 << = .05, we reject = .05, we reject HH00..
There is sufficient statistical There is sufficient statistical evidenceevidence
to infer that Metro EMS is to infer that Metro EMS is notnot meetingmeeting
the response goal of 12 minutes.the response goal of 12 minutes.
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5. Determine whether to reject 5. Determine whether to reject HH00..
There is sufficient statistical There is sufficient statistical evidenceevidence
to infer that Metro EMS is to infer that Metro EMS is notnot meetingmeeting
the response goal of 12 minutes.the response goal of 12 minutes.
Because 2.47 Because 2.47 >> 1.645, we reject 1.645, we reject HH00..
Critical Value ApproachCritical Value Approach
One-Tailed Tests About a Population One-Tailed Tests About a Population Mean:Mean:
KnownKnown
For For = .05, = .05, zz.05.05 = 1.645 = 1.645
4. Determine the critical value and rejection rule.4. Determine the critical value and rejection rule.
Reject Reject HH00 if if zz >> 1.645 1.645
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pp-Value Approach to-Value Approach toTwo-Tailed Hypothesis TestingTwo-Tailed Hypothesis Testing
The rejection rule:The rejection rule: Reject Reject HH00 if the if the pp-value -value << ..
Compute the Compute the pp-value-value using the following three steps: using the following three steps:
3. Double the tail area obtained in step 2 to obtain3. Double the tail area obtained in step 2 to obtain the the pp –value. –value.
2. If 2. If zz is in the upper tail ( is in the upper tail (zz > 0), find the area under > 0), find the area under the standard normal curve to the right of the standard normal curve to the right of zz.. If If zz is in the lower tail ( is in the lower tail (zz < 0), find the area under < 0), find the area under the standard normal curve to the left of the standard normal curve to the left of zz..
1. Compute the value of the test statistic 1. Compute the value of the test statistic zz..
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Critical Value Approach to Critical Value Approach to Two-Tailed Hypothesis TestingTwo-Tailed Hypothesis Testing
The critical values will occur in both the lower andThe critical values will occur in both the lower and upper tails of the standard normal curve.upper tails of the standard normal curve.
The rejection rule is:The rejection rule is:
Reject Reject HH00 if if zz << - -zz/2/2 or or zz >> zz/2/2..
Use the standard normal probability Use the standard normal probability distributiondistribution table to find table to find zz/2/2 (the (the zz-value with an area of -value with an area of /2 in/2 in the upper tail of the distribution).the upper tail of the distribution).
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Example: Glow ToothpasteExample: Glow Toothpaste
Two-Tailed Test About a Population Mean: Two-Tailed Test About a Population Mean: Known Known
oz.
GlowGlow
Quality assurance procedures call forQuality assurance procedures call forthe continuation of the filling process if thethe continuation of the filling process if thesample results are consistent with the assumption thatsample results are consistent with the assumption thatthe mean filling weight for the population of toothpastethe mean filling weight for the population of toothpastetubes is 6 oz.; otherwise the process will be adjusted.tubes is 6 oz.; otherwise the process will be adjusted.
The production line for Glow toothpasteThe production line for Glow toothpasteis designed to fill tubes with a mean weightis designed to fill tubes with a mean weightof 6 oz. Periodically, a sample of 30 tubesof 6 oz. Periodically, a sample of 30 tubeswill be selected in order to check thewill be selected in order to check thefilling process.filling process.
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Example: Glow ToothpasteExample: Glow Toothpaste
Two-Tailed Test About a Population Mean: Two-Tailed Test About a Population Mean: KnownKnown
oz.
GlowGlow Perform a hypothesis test, at the .03Perform a hypothesis test, at the .03level of significance, to help determinelevel of significance, to help determinewhether the filling process should continuewhether the filling process should continueoperating or be stopped and corrected.operating or be stopped and corrected.
Assume that a sample of 30 toothpasteAssume that a sample of 30 toothpastetubes provides a sample mean of 6.1 oz.tubes provides a sample mean of 6.1 oz.The population standard deviation is The population standard deviation is believed to be 0.2 oz.believed to be 0.2 oz.
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1. Determine the hypotheses.1. Determine the hypotheses.
2. Specify the level of significance.2. Specify the level of significance.
3. Compute the value of the test statistic.3. Compute the value of the test statistic.
= .03= .03
pp –Value and Critical Value Approaches –Value and Critical Value Approaches
GloGloww
HH00: :
HHaa:: 6 6
Two-Tailed Tests About a Population Two-Tailed Tests About a Population Mean:Mean:
KnownKnown
0 6.1 6
2.74/ .2/ 30
xz
n
0 6.1 6
2.74/ .2/ 30
xz
n
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GloGloww
Two-Tailed Tests About a Population Two-Tailed Tests About a Population Mean:Mean:
KnownKnown
5. Determine whether to reject 5. Determine whether to reject HH00..
pp –Value Approach –Value Approach
4. Compute the 4. Compute the pp –value. –value.
For For zz = 2.74, cumulative probability = .9969 = 2.74, cumulative probability = .9969
pp–value = 2(1 –value = 2(1 .9969) = .0062 .9969) = .0062
Because Because pp–value = .0062 –value = .0062 << = .03, we reject = .03, we reject HH00..
There is sufficient statistical evidence toThere is sufficient statistical evidence toreject the null hypothesisreject the null hypothesis
(i.e. the mean filling weight is not 6 (i.e. the mean filling weight is not 6 ounces).ounces).
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Critical Value ApproachCritical Value Approach
GloGloww
Two-Tailed Tests About a Population Two-Tailed Tests About a Population Mean:Mean:
KnownKnown
5. Determine whether to reject 5. Determine whether to reject HH00..
There is sufficient statistical evidence toThere is sufficient statistical evidence toinfer that the alternative hypothesis is infer that the alternative hypothesis is
truetrue (i.e. the mean filling weight is not 6 (i.e. the mean filling weight is not 6
ounces).ounces).
Because 2.74 Because 2.74 >> 2.17, we reject 2.17, we reject HH00..
For For /2 = .03/2 = .015, /2 = .03/2 = .015, zz.015.015 = 2.17 = 2.17
4. Determine the critical value and rejection rule.4. Determine the critical value and rejection rule.
Reject Reject HH00 if if zz << -2.17 or -2.17 or zz >> 2.17 2.17
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Confidence Interval Approach toConfidence Interval Approach toTwo-Tailed Tests About a Population MeanTwo-Tailed Tests About a Population Mean Select a simple random sample from the populationSelect a simple random sample from the population and use the value of the sample mean to developand use the value of the sample mean to develop the confidence interval for the population mean the confidence interval for the population mean .. (Confidence intervals are covered in Chapter 8.)(Confidence intervals are covered in Chapter 8.)
xx
If the confidence interval contains the hypothesizedIf the confidence interval contains the hypothesized value value 00, do not reject , do not reject HH00. Otherwise, reject . Otherwise, reject HH00..
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The 97% confidence interval for The 97% confidence interval for is is
/ 2 6.1 2.17(.2 30) 6.1 .07924x zn
/ 2 6.1 2.17(.2 30) 6.1 .07924x zn
Confidence Interval Approach toConfidence Interval Approach toTwo-Tailed Tests About a Population MeanTwo-Tailed Tests About a Population Mean
GloGloww
Because the hypothesized value for theBecause the hypothesized value for the
population mean, population mean, 00 = 6, is not in this interval, = 6, is not in this interval,the hypothesis-testing conclusion is that thethe hypothesis-testing conclusion is that the
null hypothesis, null hypothesis, HH00: : = 6, can be rejected. = 6, can be rejected.
or 6.02076 to 6.17924or 6.02076 to 6.17924
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Test StatisticTest Statistic
Tests About a Population Mean:Tests About a Population Mean: Unknown Unknown
txs n
0/
txs n
0/
This test statistic has a This test statistic has a tt distribution distribution with with nn - 1 degrees of freedom. - 1 degrees of freedom.
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Rejection Rule: Rejection Rule: pp -Value Approach -Value Approach
HH00: : Reject Reject HH0 0 if if tt >> tt
Reject Reject HH0 0 if if tt << - -tt
Reject Reject HH0 0 if if tt << - - tt or or tt >> tt
HH00: :
HH00: :
Tests About a Population Mean:Tests About a Population Mean: Unknown Unknown
Rejection Rule: Critical Value ApproachRejection Rule: Critical Value Approach
Reject Reject HH0 0 if if p p –value –value <<
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p p -Values and the -Values and the tt Distribution Distribution
The format of the The format of the tt distribution table provided in most distribution table provided in most statistics textbooks does not have sufficient detailstatistics textbooks does not have sufficient detail to determine the to determine the exactexact p p-value for a hypothesis test.-value for a hypothesis test.
An advantage of computer software packages is thatAn advantage of computer software packages is that the computer output will provide the the computer output will provide the pp-value for the-value for the tt distribution. distribution.
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A State Highway Patrol periodically samplesA State Highway Patrol periodically samples
vehicle speeds at various locationsvehicle speeds at various locations
on a particular roadway. on a particular roadway.
The sample of vehicle speedsThe sample of vehicle speeds
is used to test the hypothesisis used to test the hypothesis
Example: Highway PatrolExample: Highway Patrol
One-Tailed Test About a Population Mean: One-Tailed Test About a Population Mean: Unknown Unknown
The locations where The locations where HH00 is rejected are deemed is rejected are deemed
the best locations for radar traps.the best locations for radar traps.
HH00: : << 65 65
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Example: Highway PatrolExample: Highway Patrol
One-Tailed Test About a Population Mean: One-Tailed Test About a Population Mean: UnknownUnknown At Location F, a sample of 64 vehicles shows aAt Location F, a sample of 64 vehicles shows a
mean speed of 66.2 mph with amean speed of 66.2 mph with a
standard deviation ofstandard deviation of
4.2 mph. Use 4.2 mph. Use = .05 to = .05 to
test the hypothesis.test the hypothesis.
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One-Tailed Test About a Population Mean:One-Tailed Test About a Population Mean: Unknown Unknown
1. Determine the hypotheses.1. Determine the hypotheses.
2. Specify the level of significance.2. Specify the level of significance.
3. Compute the value of the test statistic.3. Compute the value of the test statistic.
= .05= .05
pp –Value and Critical Value Approaches –Value and Critical Value Approaches
HH00: : << 65 65
HHaa: : > 65 > 65
0 66.2 65
2.286/ 4.2/ 64
xt
s n
0 66.2 65
2.286/ 4.2/ 64
xt
s n
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One-Tailed Test About a Population Mean:One-Tailed Test About a Population Mean: Unknown Unknown
pp –Value Approach –Value Approach
5. Determine whether to reject 5. Determine whether to reject HH00..
4. Compute the 4. Compute the pp –value. –value.
Use the TDIST function in Excel to find that, for Use the TDIST function in Excel to find that, for tt = 2.286, = 2.286, the the pp–value is 0.0128–value is 0.0128
Because Because pp–value –value << = .05, we reject = .05, we reject HH00..
We are at least 95% confident that the mean We are at least 95% confident that the mean speedspeed of vehicles at Location F is greater than 65 of vehicles at Location F is greater than 65 mph.mph.
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Critical Value ApproachCritical Value Approach
5. Determine whether to reject 5. Determine whether to reject HH00..
We are at least 95% confident that the mean We are at least 95% confident that the mean speed of vehicles at Location F is greater speed of vehicles at Location F is greater than 65 mph. Location F is a good candidate than 65 mph. Location F is a good candidate for a radar trap.for a radar trap.
Because 2.286 Because 2.286 >> 1.669, we reject 1.669, we reject HH00..
One-Tailed Test About a Population Mean:One-Tailed Test About a Population Mean: Unknown Unknown
For For = .05 and d.f. = 64 – 1 = 63, = .05 and d.f. = 64 – 1 = 63, tt.05.05 = 1.669 = 1.669
4. Determine the critical value and rejection rule.4. Determine the critical value and rejection rule.
Reject Reject HH00 if if tt >> 1.669 1.669
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The equality part of the hypotheses always appearsThe equality part of the hypotheses always appears in the null hypothesis.in the null hypothesis. In general, a hypothesis test about the value of aIn general, a hypothesis test about the value of a population proportion population proportion pp must take one of themust take one of the
following three forms (where following three forms (where pp00 is the hypothesized is the hypothesized
value of the population proportion).value of the population proportion).
A Summary of Forms for Null and A Summary of Forms for Null and Alternative Hypotheses About a Alternative Hypotheses About a
Population ProportionPopulation Proportion
One-tailedOne-tailed(lower tail)(lower tail)
One-tailedOne-tailed(upper tail)(upper tail)
Two-tailedTwo-tailed
0 0: H p p0 0: H p p
0: aH p p 0: aH p p0: aH p p 0: aH p p0 0: H p p0 0: H p p 0 0: H p p0 0: H p p
0: aH p p 0: aH p p
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Test StatisticTest Statistic
zp p
p
0
z
p p
p
0
pp p
n 0 01( ) pp p
n 0 01( )
Tests About a Population ProportionTests About a Population Proportion
where:where:
assuming assuming npnp >> 5 and 5 and nn(1 – (1 – pp) ) >> 5 5
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Rejection Rule: Rejection Rule: pp –Value Approach –Value Approach
HH00: : pppp Reject Reject HH0 0 if if zz >> zz
Reject Reject HH0 0 if if zz << - -zz
Reject Reject HH0 0 if if zz << - -zz or or zz >> zz
HH00: : pppp
HH00: : pppp
Tests About a Population ProportionTests About a Population Proportion
Reject Reject HH0 0 if if p p –value –value <<
Rejection Rule: Critical Value ApproachRejection Rule: Critical Value Approach
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Example: National Safety Council Example: National Safety Council (NSC)(NSC) For a Christmas and New Year’s week, theFor a Christmas and New Year’s week, the
National Safety Council estimated thatNational Safety Council estimated that
500 people would be killed and 25,000500 people would be killed and 25,000
injured on the nation’s roads. Theinjured on the nation’s roads. The
NSC claimed that 50% of theNSC claimed that 50% of the
accidents would be caused byaccidents would be caused by
drunk driving.drunk driving.
Two-Tailed Test About aTwo-Tailed Test About aPopulation ProportionPopulation Proportion
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A sample of 120 accidents showed thatA sample of 120 accidents showed that
67 were caused by drunk driving. Use67 were caused by drunk driving. Use
these data to test the NSC’s claim withthese data to test the NSC’s claim with
= .05.= .05.
Two-Tailed Test About aTwo-Tailed Test About aPopulation ProportionPopulation Proportion
Example: National Safety Council (NSC)Example: National Safety Council (NSC)
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Two-Tailed Test About aTwo-Tailed Test About aPopulation ProportionPopulation Proportion
1. Determine the hypotheses.1. Determine the hypotheses.
2. Specify the level of significance.2. Specify the level of significance.
3. Compute the value of the test statistic.3. Compute the value of the test statistic.
= .05= .05
pp –Value and Critical Value Approaches –Value and Critical Value Approaches
0: .5H p0: .5H p: .5aH p: .5aH p
0 (67/ 120) .5 1.28
.045644p
p pz
0 (67/ 120) .5 1.28
.045644p
p pz
0 0(1 ) .5(1 .5).045644
120p
p p
n
0 0(1 ) .5(1 .5)
.045644120p
p p
n
a commona commonerror is error is usingusing
in this in this formula formula
pp
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ppValue ApproachValue Approach
4. Compute the 4. Compute the pp -value. -value.
5. Determine whether to reject 5. Determine whether to reject HH00..
Because Because pp–value = .2006 > –value = .2006 > = .05, we cannot reject = .05, we cannot reject HH00..
Two-Tailed Test About aTwo-Tailed Test About aPopulation ProportionPopulation Proportion
For For zz = 1.28, cumulative probability = .8997 = 1.28, cumulative probability = .8997
pp–value = 2(1 –value = 2(1 .8997) = .2006 .8997) = .2006
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Two-Tailed Test About aTwo-Tailed Test About aPopulation ProportionPopulation Proportion
Critical Value ApproachCritical Value Approach
5. Determine whether to reject 5. Determine whether to reject HH00..
For For /2 = .05/2 = .025, /2 = .05/2 = .025, zz.025.025 = 1.96 = 1.96
4. Determine the criticals value and 4. Determine the criticals value and rejection rule.rejection rule.
Reject Reject HH00 if if zz << -1.96 or -1.96 or zz >> 1.96 1.96
Because 1.278 > -1.96 and < 1.96, we cannot reject Because 1.278 > -1.96 and < 1.96, we cannot reject HH00..