Two analysts took repeated readings on the hardness of city water. Assuming that the readings of analyst i constitute a sample from a normal population having variance 2 i , i = 1, 2, compute a 95 percent two-sided confidence interval for 2 1 /2 2 when the data are as follows: Coded Measures of Hardness Analyst 1 Analyst 2 .46 .82 .62 .61 .37 .89 .40 .51 .44 .33 .58 .48 .48 .23 .53 .25 .67 .88

Chapter 9 Proportions: Sampling Distributions & Confidence Intervals Sampling Distribution of a Sample Proportion Understand the difference between a parameter and a statistic (discussed in Chapter 8). In most chapters you will be asked to identify the parameter of interest in a problem. This Chapter also introduces the important concept of sampling distributions. Parameters (some examples) Statistics µ population mean (mu) y sample mean (ybar) σ population standard deviation (sigma) s sample standard deviation p population proportion p sample proportion (phat) ρ population correlation coefficient (rho)