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CHAPTER 7.1 Confidence Intervals for the mean

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ESTIMATION Estimation is one aspect of inferential statistics. It is the process of estimating the value of a parameter from information obtained from a sample. It is assumed that the samples are randomly selected. Another is that they meet the requirements for the central limit theorem.

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POINT ESTIMATE A point estimate is a specific numerical value estimate of a parameter. The best point estimate of the population mean μ is the sample mean X for example, a college surveys 100 students taking a particular class on their age. The mean age is 22.3 years

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PROPERTIES OF A GOOD ESTIMATOR 1.Unbiased 2.Consistent 3.Relatively efficient (smallest variance)

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INTERVAL ESTIMATE An interval estimate of a parameter is an interval or a range of values used to estimate the parameter. This estimate may or may not contain the value of the parameter being estimated. For example 21.9 < μ < 22.9 or 22.3

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CONFIDENCE LEVEL The confidence level of an interval estimate of a parameter is the probability that the interval estimate will contain the parameter, assuming that a large number of samples are selected and that the estimation process on the same parameter is repeated.

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CONFIDENCE INTERVAL A confidence interval is a specific interval estimate of a parameter determined by using data obtained from a sample and by using the specific confidence level of the estimate.

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MOST COMMON CONFIDENCE INTERVALS The three most common confidence intervals are: 90%, 95%, 99% For a 90% confidence interval, use the value 1.65 For a 95% confidence interval, use the value 1.96 For a 99% confidence interval, use the value 2.58

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ALPHA The symbol is used in the general formula for confidence intervals α (alpha) represents the total area in each one of the tails

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MARGIN OF ERROR The margin of error, aka maximum error of the estimate, is the maximum likely difference between the point estimate of a parameter and the actual value of the parameter The margin of error is represented by

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FORMULA FOR CONFIDENCE INTERVALS OF THE MEAN FOR A SPECIFIC

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DAYS IT TAKES TO SELL AN AVEO A researcher wishes to estimate the number of days it takes an automobile dealer to sell a Chevy Aveo. A sample of 50 cars had a mean time on the dealer’s lot of 54 days. Assumer the population standard deviation to be 6.0 days. Find the best point estimate of the population mean and the 95% confidence interval of the population mean.

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WAITING TIMES IN AN EMERGENCY ROOM A survey of 30 emergency room patients found that the average waiting time for treatment was 174.3 minutes. Assuming that the population standard deviation is 46.5 minutes, find the best point estimate of the population mean and the 99% confidence interval of the population mean.

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CREDIT UNION ASSETS The following data represent a sample of the assets (in millions of dollars) of 30 credit unions in southwestern Pennsylvania. Find the 90% confidence interval of the mean. 12.232.8913.1973.2511.598.747.9240.225.012.27 16.561.249.161.916.693.174.782.421.4712.77 4.392.171.4214.641.0618.1316.8521.5812.242.76

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APPLYING THE CONCEPTS Pg. 363 #1-5

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Chapter 7 Confidence Intervals and Sample Size © Copyright McGraw-Hill 2000 7-1.

Chapter 7 Confidence Intervals and Sample Size © Copyright McGraw-Hill 2000 7-1.

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