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BUS310_L17_3.15.11

# BUS310_L17_3.15.11 - Inferential Statistics Hypothesis...

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Lecture 17: Inferential Statistics / Hypothesis Testing II
PS4

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‘COLA S Chapter 14, Question 2 (Problem 14.6) Process is out of control (Rule 1: Outlier below the Lower Control Limit, Rule 2: 8 consecutive points above the mean)
a) Confidence Interval Estimation with PHStat ‘Confidence Intervals’ The mean minimum deposit to open an account for all banks is estimated as \$56.52 based on the sample. We can be 95% confident that the population mean falls between \$31.51 and \$81.53 (If the assumption of normality is confirmed) BANKCOST1.xls PHStat, ‘Confidence Intervals’, ‘Estimate for the Mean, sigma unknown’

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Assumptions (What do you need to know to make this estimate valid?) Sample size is large (n>30) Data is normal Check Skewness and Kurtosis for normality: à Distribution is NOT normal à Assumption is NOT valid In this case, the estimate is not valid. We have to increase BANKCOST1.xls
a) Confidence Interval Estimation with PHStat ‘Confidence Intervals’ The mean bounced check fee for all banks is estimated as \$23 based on the sample. We can be 95% confident that the population mean falls between \$21.01 and \$24.99 (if the assumptions are met and the t-test is valid) BANKCOST1.xls PHStat, ‘Confidence Intervals’, ‘Estimate for the Mean, sigma unknown’

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B) Assumptions (What do you need to know to make this estimate valid?) Sample size is large (n>30) Data is normal Check Skewness and Kurtosis for normality: à Distribution is approximately normal à Assumption is valid Also use BANKCOST1.xls
Problem Set 4 (Chapter 8: Confidence Intervals) 5. (2 points) Problem 8.26 In a survey, 27% of small business owners indicated that they never check in with the office when on vacation. The article did not disclose the sample size used in the study. a) Suppose that the survey was based on 500 small business owners. Construct a 95% confidence interval estimate for the population proportion of small business owners who never check in with the office when on vacation b) Do the same for a sample of 1000 small business owners. c) Discuss the effect of sample size on the confidence interval estimate. PHStat, ‘Confidence Intervals’, ‘Estimate for the Proportion’

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Sample Size 500: Proportion between 23% and 31%. à The larger the sample size, the narrower the confidence interval c) Discuss the effect of sample size on the confidence interval estimate. Sample Size 1000: Proportion between 24% and 30%. CI specifically accommodates variability connected to this sample size
Outline Review Chapter 10: Hypothesis Testing with ANOVA (2 categories) Review Chapter 8, 9, 10 with an example Are the means of three or more populations different? H1: Not all μj are equal H0: μ1 = μ2 = … = μc (the c population means are equal) Compare means of the numerical variable across categories Are the means of population one and two different?

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