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Confidence Interval

Confidence interval for average value for prescriptions

The BelSante Company operates retail pharmacies in 10 Eastern states. Recently, the company's internal audit department selected a random sample of 300 prescriptions issued throughout the system. The objective of the sampling was to estimate the average dollar value of all prescriptions issued by the company. The following data


Probability In Excel 1. According to Investment Digest ("Diversification and the Risk/Reward Relationship", Winter 1994, 1-3), the mean of the annual return for common stocks from 1926 to 1992 was 19.4%, and the standard deviation of the annual return was 24.5%. During the same 67-year time span, the mean of the annual r

Statistics: Confidence intervals for sample; Cohen's guidelines, two-tailed test

8.22. Calculate the 95% confidence interval for the following fictional data regarding daily TV viewing habits: µ = 4.7; σ = 1.3 hours; sample of 78 people with a mean of 4.1 hours. 8.30. For each of the following d values, identify the size of the effect using Cohen's guidelines. (a) d = 0.79 (b) d = - 0.43 (c) d = 0

Statistics symbols, confidence intervals, z test

8.16. In statistics, concepts are often expressed in symbols and equations. For each of the following, (i) identify the incorrect symbol, (ii) state what the correct symbol should be, and (iii) explain why the initial symbol was incorrect: (a) Мlower =-z(σ) + Msample The incorrect symbol is σ. It should be σm because i

Calculations for Hypothesis Testing and Confidence Intervals

Please see the attached problem. A manufacturing company produces water filters for home refrigerators. The process has typically produced about 4% defective. A recently designed experiment has led to changing the seal to reduce defects. With the process running using the new seal, a random sample of 300 filters yielded 7 def

Statistics: Yaschchin discusses process for chemical etching of silicon wafers

Please see the attached problem. 2. Yaschchin (1995) discusses a process for the chemical etching of silicon wafers used in itegrated circuits. This company wishes to detect an increase in the thickness of the silicon oxide layers because thicker layers require longer etching times. Process specifications state a target valu

Statistics 4.10: Kane discusses concentricity of engine oil seal groove

See the attached problem. 4.10. Kane (1986) discusses the concentricity of an engine oil seal groove. Historically, the standard deviation for the concentricity is 0.7. The target average concentricity is 5.6. To monitor this process, he periodically takes a random sample of three measurements. a. A recent sample yielded

Statistics: estimate the proportion of the population

Part I. Suppose the coach of the football team wants to estimate the proportion of the population of fans who support his current starter lineup. The coach wants the estimate to be .04 of the true proportion. Assume a 99 percent level of confidence. The coach estimated the proportion supporting the current starter lineup to

Constructing 95 percent confidence intervals

A reporter took a simple random sample of 725 voters in a region that has a population of 12,457. He recorded that 338 of the persons polled favored Issue 1 on the ballot. Construct a 95% confidence interval for the proportion that favor the issue and then discuss what the reporter can and cannot say in his report. If you were t


1. Consider a normal population with a mean+ 25 and a standard deviation= 7.0. A. Calculate the standard score for a value x of 24. B. Calculate the standard score for a randomly selected sample of 45 with a sample mean = 25. C. Explain why the standard scores of 24 are different between A and B above. 2. Assume tha

Maximum error of estimate.

1. Consider a population with a mean =73.6 and a standard deviation=5.38 A. Calculate the z-score for sample mean=72.7 from a sample size of 45. B. Could this z-score be used in calculating probabilities using Table 3 in the Appendix B. Why or why not? 2. Given a level of confidence of 99% and a population standard deviatio

Estimate the sample size and population mean

A1) Suppose the U.S. President wants an estimate of the proportion of the population who support his current policy toward revisions in the Social Security system. The president wants the estimate to be within .04 of the true proportion. Assume a 95 percent level of confidence. The president's political advisers estimated the p

4 Statistics problems: Confidence interval estimate of mean

Q-3a. A stationery store wants to estimate the mean retail value of greeting cards purchased by its customers when they visit the store. A random sample of 15 customers indicates a mean amount of $2.55 with a standard deviation of $0.44 per customer per visit. Assuming a normal distribution, construct a 95% confidence inter

Confidence Interval - statistics

A survey of individuals who passed the BAR finds the average starting salary for lawyers to be $75,215 for 36 individuals sampled. If the population standard deviation is $15,990 find a 90% confidence interval for the true mean. Round your answers to the nearest whole number.

Hypothesis testing: wealth

Is there any difference between the proportion of Americans who wish they were rich and the proportion of Canadians who wish they were rich? A random sample of 1000 Americans showed that 550 wish they were rich, while a random sample of 500 Canadians showed that 225 wished they were rich. a. Find a 97.5% confidence interval f

Statistics Problems

1. Given a normal distribution with mean,m =100 and standard deviation, s = 10, if you select a sample of n=25, what is the probability that x is a. less than 95? b. between 95 and 97.5? c. above 102.2? d. There is a 65% chance that X is above what value? 2. Time spent using e-mail per session is normally distri

Finding the confidence interval for poll or survey results

Quality Progress, Feburary 2005, reports on the results achieved by Bank of America in improving customer satisfaction and customer loyalty by listening to the "voice of the customer". A key measure of customer satisfaction is the response on a scale from 1 to 10 to the question: "Considering all the business you do with Bank of

Formulate an 84% interval estimate for a true proportion

1) The Target Corporation personnel director wants to estimate the number of employees within one year of retirement. A random sample of 120 employee records is selected, and 36 people are found to be within one year of retirement. Formulate an 84% interval estimate for the true proportion of employees within one year of retir

Statistics Problems: Mean, probability, standard deviation, confidence interval

1. You are a manager of a Starbucks located at Southcenter Mall. Recently, a new local coffee shop specializing in lattes has opened in the Mall. You are wondering what the impact on your latte sales may be. You know from previous data tracking that the largest number of lattes sold at your location is during the morning. T

Bank customer and bank manager

In the bank customer waiting time case, a bank manager had developed a new system to reduce the time customers spend waiting to be served by tellers during peak business hours. Typical waiting times during peak business hours under the current ystem are roughly 9 to 10 minutes The bank manager hopes that the new system will lo

Confidence Intervals: New type of ammunition, measured velocity

Fifty rounds of a new type of ammunition was fired from a M-1, and the muzzle velocity of the projectile was measured. The sample had a mean velocity of 853 meters per second, with a standard deviation of 2.9 meters per second How do you know which Hypothesis Testing to use? A) Construct and interpret a 99% Confidence In