Estimating Population Values参考.ppt

Chapter 7Estimating Population Values Chapter Goals After completing this chapter, you should be able to: Distinguish between a point estimate and a confidence interval estimate Construct and interpret a confidence interval estimate for a single population mean using both the z and t distributions Determine the required sample size to estimate a single population mean within a specified margin of error Form and interpret a confidence interval estimate for a single population proportion Confidence Intervals Content of this chapter Confidence Intervals for the Population Mean, ? when Population Standard Deviation ? is Known when Population Standard Deviation ? is Unknown Determining the Required Sample Size Confidence Intervals for the Population Proportion, p Point and Interval Estimates A point estimate is a single number, a confidence interval provides additional information about variability Point Estimates Confidence Intervals How much uncertainty is associated with a point estimate of a population parameter? An interval estimate provides more information about a population characteristic than does a point estimate Such interval estimates are called confidence intervals Confidence Interval Estimate An interval gives a range of values: Takes into consideration variation in sample statistics from sample to sample Based on observation from 1 sample Gives information about closeness to unknown population parameters Stated in terms of level of confidence Never 100% sure Estimation Process General Formula The general formula for all confidence intervals is: Confidence Level Confidence Level Confidence in which the interval will contain the unknown population parameter A percentage (less than 100%) Confidence Level, (1-?) Suppose confidence level = 95% Also written (1 - ?) = .95 A relative frequency interpretation: In the long run, 95% of all the confidence intervals that can be constructed will contain the unknown true parameter A specific interval either will