Exam 7: Inferences Based on a Single Sample: 355 Tests of Hypotheses

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A method currently used by doctors to screen women for possible breast cancer fails to detect cancer in 20% of women who actually have the disease. A new method has been developed that researchers hope will be able to detect cancer more accurately. A random sample of 80 women known to have breast cancer were screened using the new method. Of these, the new method failed to detect cancer in 9. Is the sample size sufficiently large to conduct this test of hypothesis? Explain.

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Consider the following printout. HYPOTHESIS: VARIANCE X=xX = x X=gpaX = g p a SAMPLE MEAN OF X =2.2602= 2.2602 SAMPLE VARIANCE OF X=.19000X = .19000 SAMPLE SIZE OF X =198= 198 HYPOTHESIZED VALUE (x)=2.4( x ) = 2.4 VARIANCE Xx=.1398X - x = - .1398 z=4.51298z = - 4.51298 State the proper conclusion when testing H0:μ=2.4H _ { 0 } : \mu = 2.4 vs. Ha:μ<2.4H _ { \mathrm { a } } : \mu < 2.4 at α=.05\alpha = .05 .

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The null distribution is the distribution of the test statistic assuming the null hypothesis is true; it mound shaped and symmetric about the null mean μ0\mu _0 .

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A small private college is interested in determining the percentage of its students who live off campus and drive to class. Specifically, it was desired to determine if less than 20% of their current Students live off campus and drive to class. A sample of 108 students was randomly selected and the following printout was obtained: Hypothesis Test - One Proportion Sample Size 108 Successes 16 Proportion 0.14815 Null Hypothesis: P=0.2\quad \mathrm { P } = 0.2 Alternative Hyp: P<0.2\quad \mathrm { P } < 0.2 Difference -0.05185 Standard Error 0.03418 Z -1.35 p-value 0.0885 Based on the information contained in the printout, what conclusion would be correct when testing at α=0.05\alpha = 0.05 .

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The rejection region refers to the values of the test statistic for which we will reject the alternative hypothesis.

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The smaller the p-value in a test of hypothesis, the more significant the results are.

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The owner of Get-A-Away Travel has recently surveyed a random sample of 183 customers to determine whether the mean age of the agency's customers is over 32 . The appropriate hypotheses are H0:μ=32,Ha:μ>32H _ { 0 } : \mu = 32 , H _ { \mathrm { a } } : \mu > 32 . If he concludes the mean age is over 32 when it is not, he makes a __________error. If he concludes the mean age is not over 32 when it is, he makes a _______error.

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Find the rejection region for the specified hypothesis test. -Consider a test of H0:μ=9\mathrm { H } _ { 0 } : \mu = 9 . For the following case, give the rejection region for the test in terms of the zz -statistic: Ha:μ>9,α=0.01\mathrm { H } _ { \mathrm { a } } : \mu > 9 , \alpha = 0.01

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A test of hypothesis was performed to determine if the true proportion of college students who preferred a particular brand of soda differs from .50. The ASP printout is supplied below. Note: All data refer to the proportion of students who preferred the brand of soda.  HYPOTHESIS: PROPORTION X =x\text { HYPOTHESIS: PROPORTION X }=\mathrm{x} X=drink(soda=1)X=\operatorname{drink}-(\operatorname{soda}=1) SAMPLE PROPORTION OF X =.407186 SAMPLE SIZE OF X =167 HYPOTHESIZED VALUE (x) =.5  SAMPLEPROPORTION xx=.092814\text { SAMPLEPROPORTION } x-x=-.092814 =-2.39884 P-VALUE =.0164 P-VALUE /2 =.0082 SD. ERROR =.0386912 State the proper conclusion if the test was conducted at α=,10\alpha = , 10

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A random sample of n=15n = 15 observations is selected from a normal population to test H0:μ=2.89H _ { 0 } : \mu = 2.89 against Ha:μ<2.89H _ { \mathrm { a } } : \mu < 2.89 at α=.01\alpha = .01 . Specify the rejection region.

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A consumer product magazine recently ran a story concerning the increasing prices of digital cameras. The story stated that digital camera prices dipped a couple of years ago, but now are beginning to increase in price because of added features. According to the story, the average price of all digital cameras a couple of years ago was $215.00. A random sample of cameras was recently taken and entered into a spreadsheet. It was desired to test to determine if that average price of all digital cameras is now more than $215.00. The information was entered into a spreadsheet and the following printout was obtained: One-Sample T Test Null Hypothesis: μ=215\mu = 215 Alternative Hyp: μ>215\mu > 215  A consumer product magazine recently ran a story concerning the increasing prices of digital cameras. The story stated that digital camera prices dipped a couple of years ago, but now are beginning to increase in price because of added features. According to the story, the average price of all digital cameras a couple of years ago was $215.00. A random sample of cameras was recently taken and entered into a spreadsheet. It was desired to test to determine if that average price of all digital cameras is now more than $215.00. The information was entered into a spreadsheet and the following printout was obtained: One-Sample T Test  Null Hypothesis:  \mu = 215  Alternative Hyp:  \mu > 215      Cases Included 22  Is a sample size  n = 22  large enough to utilize the central limit theorem in this inferential procedure? Cases Included 22 Is a sample size n=22n = 22 large enough to utilize the central limit theorem in this inferential procedure?

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How many tissues should a package of tissues contain? Researchers have determined that a person uses an average of 41 tissues during a cold. Suppose a random sample of 10,000 people yielded the following data on the number of tissues used during a cold: xˉ=35,s=18\bar { x } = 35 , s = 18 . Identify the null and alternative hypothesis for a test to determine if the mean number of tissues used during a cold is less than 41.41 .

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A large university is interested in learning about the average time it takes students to drive to campus. The university sampled 51 students and asked each to provide the amount of time they spent traveling to campus. The sample results found that the sample mean was 23.24323.243 minutes and the sample standard deviation was 20.4020.40 minutes. It is desired to determine if the population standard deviation exceeds 20 minutes. Calculate the test statistic for this test of hypothesis.

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Data were collected from the sale of 25 properties by a local real estate agent. The following printout concentrated on the land value variable from the sampled properties. HYPOTHESIS: MEAN X =x= x X = land - value SAMPLE MEAN OF X =50,740 SAMPLE VARIANCE OF X =273,643,254 SAMPLE SIZE OF X =25 x =46,297 MEANX- =4443 =1.34293 D.F. =24 P-VALUE =0.1918585 P -VALUE /2 =0.0959288 SD. ERROR =3308.43 Find the pp -value for testing whether the mean land value differs from $46,297\$ 46,297 .

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We never conclude "Accept H0\mathrm { H } _ { 0 } " in a test of hypothesis. This is because:

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Based on the information in the screen below, what would you conclude in the test of H0:μ14,Ha:μ>14. Use α=.01H _ { 0 } : \mu \leq 14 , H _ { \mathrm { a } } : \mu > 14 \text {. Use } \alpha = .01 \text {. }  Based on the information in the screen below, what would you conclude in the test of  H _ { 0 } : \mu \leq 14 , H _ { \mathrm { a } } : \mu > 14 \text {. Use } \alpha = .01 \text {. }

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The hypotheses for H0:μ=125.4 and Ha:μ125.4 are tested at α=.10. Sketch the H _ { 0 } : \mu = 125.4 \text { and } H _ { \mathrm { a } } : \mu \neq 125.4 \text { are tested at } \alpha = .10 \text {. Sketch the } appropriate rejection region.

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A supermarket sells rotisserie chicken at a fixed price per chicken rather than by the weight of the chicken. The store advertises that the average weight of their chickens is 4.6 pounds. A random sample of 30 of the store's chickens yielded the weights (in pounds) shown below. 4.4 4.7 4.6 4.4 4.5 4.3 4.6 4.5 4.6 4.9 4.6 4.8 4.3 4.4 4.7 4.5 4.2 4.3 4.1 4.0 4.5 4.6 4.2 4.4 4.7 4.8 5.0 4.2 4.1 4.5 Test whether the population mean weight of the chickens is less than 4.6 pounds. Use α=.05.\alpha = .05 .

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Under the assumption that μ=μa\mu = \mu _ { \mathrm { a } } , where μa\mu _ { \mathrm { a } } is the alternative mean, the distribution of xˉ\bar { x } is mound shaped and symmetric about μa\mu _ { \mathrm { a } } .

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It is desired to test H0: µ = 50 against HA: µ ? 50 using ? = 0.10. The population in question is uniformly distributed with a standard deviation of 15. A random sample of 49 will be drawn from this population. If µ is really equal to 48, what is the probability that the hypothesis test would lead the investigator to commit a Type II error?

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