Concept explainers
Increases in Customer Satisfaction. Will improving customer service result in higher stock prices for the companies providing the better service? “When a company’s satisfaction score has improved over the prior year’s results and is above the national average (75.7), studies show its shares have a good chance of outperforming the broad stock market in the long run.” The following satisfaction scores of three companies for the 4th quarters of two previous years were obtained from the American Customer Satisfaction Index. Assume that the scores are based on a poll of 60 customers from each company. Because the polling has been done for several years, the standard deviation can be assumed to equal 6 points in each case.
- For Rite Aid, is the increase in the satisfaction score from year 1 to year 2 statistically significant? Use α = .05. What can you conclude?
- Can you conclude that the year 2 score for Rite Aid is above the national average of 75.7? Use α = .05.
- For Expedia, is the increase from year 1 to year 2 statistically significant? Use α = .05.
- When conducting a hypothesis test with the values given for the standard deviation, sample size, and α, how large must the increase from year 1 to year 2 be for it to be statistically significant?
- Use the result of part (d) to state whether the increase for J.C. Penney from year 1 to year 2 is statistically significant.
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- One bulb manufacturer claims an average bulb life of 1,600 hours. It is suspected that the actual average is significantly lower. To verify this, a sample of 49 bulbs is selected and the life of each bulb is measured. A sample mean of 1,500 hours and a standard deviation of 120 hours were obtained from them. Can you be sure, at 5% significance, that the mean life is less than what the manufacturer claims?arrow_forwardThe specification calls for the dimension of a certain mechanical part to be 0.55 inches. A random sample of 35 parts taken from a large batch showed a mean 0.54 in. with a deviation of 0.05 in. Can it be concluded, at 1% significance, that the batch of parts meets the required specification?arrow_forwardA manufacturer produces a wire rope of a certain type, which has a breaking strength of not more than 300 kg. A new and cheaper process is discovered which is desired to be employed, provided that the wire rope thus produced has an average breaking strength greater than 300 kg. If a random sample of 26 wires produced with the new process has given a mean of 304.5 kg and a standard deviation of 15 kg, should the manufacturer adopt the new process?arrow_forward
- We are interested in whether the proportions of female suicide victims for ages 15 to 24 are the same between the white and the black races in the United States. We randomly pick one year to compare the races. The number of suicides estimated in the United States in that year for white females is 4,930. Five hundred eighty-three were aged 15 to 24. The estimate for black females is 330. Forty-one were aged 15 to 24. We will let female suicide victims be our population. (Use α = 0.05.) NOTE: If you are using a Student's t-distribution for the problem, including for paired data, you may assume that the underlying population is normally distributed. (In general, you must first prove that assumption, though.) Part (a) State the null hypothesis. ○ Ho: PW> PB O Ho: PW + PB Ho: Pw≤ PB Ho: PW-PB ○ Ho: Pw PB Part (c) In words, state what your random variable P'w-P'B represents. P'w-P'B represents the average difference of white and black female suicide victims, aged 15 to 24. ○ P'w-P'B…arrow_forwardplease solve this problem step by step and make it quick pleasearrow_forwardplease solve this problem step by step and make it quick pleasearrow_forward
- 8.67 Free recall memory strategy. Psychologists who study ①memory often use a measure of "free recall" (e.g., the RECALL number of correctly recalled items in a list of to-be- remembered items). The strategy used to memorize the list-for example, category clustering-is often just as important. Researchers at Central Michigan University developed an algorithm for computing measures of cat- egory clustering in Advances in Cognitive Psychology (Oct. 2012). One measure, called ratio of repetition, was recorded for a sample of 8 participants in a memory study. These ratios are listed in the table. Test the theory that the average ratio of repetition for all participants in a similar memory study differs from .5. Select an appropriate Type I error rate for your test. .25 .43 .57 .38 .38 .60 .47 .30 Source: Senkova, O., & Otani, H. "Category clustering calculator for free recall." Advances in Cognitive Psychology, Vol. 8, No. 4, Oct. 2012 (Table 3).arrow_forward8.64 Radon exposure in Egyptian tombs. Refer to the D Radiation Protection Dosimetry (Dec. 2010) study TOMBS of radon exposure in Egyptian tombs, Exercise 7.39 (p. 334). The radon levels-measured in becquerels per cubic meter (Bq/m³)-in the inner chambers of a sam- ple of 12 tombs are listed in the table. For the safety of the guards and visitors, the Egypt Tourism Authority (ETA) will temporarily close the tombs if the true mean level of radon exposure in the tombs rises to 6,000 Bq/m³. Consequently, the ETA wants to conduct a test to deter- mine if the true mean level of radon exposure in the tombs is less than 6,000 Bq/m³, using a Type I error probabil- ity of .10. A SAS analysis of the data is shown on p. 399. Specify all the elements of the test: Ho, Ha, test statistic, p-value, a, and your conclusion. 50 390 910 12100 180 580 7800 4000 3400 1300 11900 1100 N Mean Std Dev Std Err Minimum Maximum 12 3642.5 4486.9 1295.3 50.0000 12100.0arrow_forwardHow does probability help businesses make informed decisions under uncertainty? Provide an example of how businesses use probability in marketing to predict customer behavior. Why is probability considered essential in financial decision-making, particularly in portfolio management? Discuss how the use of probability in inventory management can improve customer satisfaction. Compare the role of probability in marketing and financial decision-making. How do the applications differ in their objectives?arrow_forward
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