1. Determining Sample Size

2. Chapter 13 -2 VariablePopulationSample Mean μ Proportion π p Variance Standard deviation σ s SizeNn Standard error of the mean Standard error of the proportion Standardized variate (z) Copyright © 2012 Pearson Education, Inc.

3. Confidence Interval Approach MeansProportions Chapter 13 - 3 Copyright © 2012 Pearson Education, Inc.

4. The Confidence Interval Approach. Chapter 13 - 4 z Copyright © 2012 Pearson Education, Inc.

5. The Confidence Interval Approach (Cont.) Copyright © 2012 Pearson Education, Inc. Chapter 13 - 5

6. Chapter 13 - 6 Copyright © 2012 Pearson Education, Inc. The confidence interval is given by We can now set a 95% confidence interval around the sample mean of $182. The 95% confidence interval is given by = 182.00 + 1.96(3.18) = 182.00 + 6.23 Thus the 95% confidence interval ranges from $175.77 to $188.23.

7. 0.475 Chapter 13 - 7 Copyright © 2012 Pearson Education, Inc.

8. Chapter 13 - 8 Copyright © 2012 Pearson Education, Inc. StepsMeansProportions 1. Specify the level of precision. 2. Specify the confidence level (CL). CL = 95% 3. Determine the z value associated with the CL. Z value is 1.96

9. Chapter 13 -9 Copyright © 2012 Pearson Education, Inc. StepsMeansProportions 4. Determine the standard deviation of the population Estimate σ σ = 55 Estimate π π = 0.64 5. Determine the sample size using the formula for the standard error 6. If necessary, reestimate the confidence interval by employing s to estimate σ

10. Incidence rate refers to the rate of occurrence or the percentage of persons eligible to participate in the study. In general, if there are c qualifying factors with an incidence of Q 1, Q 2, Q 3,...Q C, each expressed as a proportion, Incidence rate= Q 1 x Q 2 x Q 3....x Q C Initial sample size= Final sample size Incidence rate x Completion rate Chapter 13 - 10 Copyright © 2012 Pearson Education, Inc.

11. International Marketing Research When conducting marketing research in foreign countries, statistical estimation of sample size can be difficult, because estimates of the population variance might be unavailable. When statistical estimation of sample size is attempted, the differences in estimates of population variance should be recognized and factored in, if possible. When the goal is to examine differences across countries or international markets, it is desirable to have the same sample size across countries. Copyright © 2012 Pearson Education, Inc. Chapter 13 - 11