1. 1 Marketing Research Aaker, Kumar, Day Ninth Edition Instructor’s Presentation Slides

2. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/2 Chapter Fifteen Sample Size and Statistical Theory

3. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/3 Determining the Sample Size Ad Hoc Methods Used when a person knows from experience what sample size to adopt Used when budgetary constraints dictate the size of the sample Rule of Thumb Sample should be large enough, so that when divided into groups, each group will have a minimum sample size of 100 or more If analysis involves comparison between subgroups, sample size in each subgroup should be 20 to 50 Use disproportionate sampling if one of groups of population is relatively small

4. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/4 Determining the Sample Size (contd.) Budget Constraints Researcher must decide whether sample size dictated by budget constraints allows a worthwhile study to be conducted Comparative Studies Find similar studies and use their sample sizes as a guide

5. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/5 Factors Determining Sample Size Number of groups and subgroups within the sample Value of information in the study Accuracy level required in results Cost of sample Variability of the population

6. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/6 Population Characteristics/Parameters Population Mean Normally unknown Determine value as closely as possible by taking a sample from population Population Variance Measure of population dispersion Based on degree to which a response differs from population average response The difference of each value from its mean is squared and averaged across all responses

7. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/7 Population Characteristics/ parameters The population opinion on symphony starting time (7:30 P.M. on weekdays)

8. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/8 Sample Characteristics/Statistics Sample mean ( ) is used to estimate the unknown population mean Example: A sample of symphony season-ticket holders

9. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/9 Sample Characteristics/Statistics (contd.) Sample mean

10. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/10 Sample Reliability X will vary from sample to sample As sample size (n) increases, variation in X will decrease standard error of decreases as the sample size gets larger

11. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/11 Sampling Distribution The normal distribution of Indicates probability of getting a particular sample mean

12. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/12 Sampling Distribution (contd.) The effect of increasing sample size on the normal distribution of

13. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/13 Interval Estimation varies from sample to sample The difference between the sample mean ( ) and the population mean is the sampling error Interval size depends on the confidence level the researcher wants for the interval to contain the true population mean If the population standard deviation is not known, it is necessary to estimate it with the sample standard deviation

14. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/14 Interval Estimation

15. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/15 Interval Estimation (contd.) Size of Interval Estimate depends on : Confidence level Population standard deviation Sample size

16. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/16 Sample Size Question Size of the sampling error that is desired Confidence level Expected variance

17. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/17 Determining the Population Standard Deviation Options: Use a sample standard deviation obtained from a previous comparable survey or from a pilot survey Estimate the sample standard deviation (s) subjectively

18. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/18 Proportions Population variance,

19. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/19 Proportions (contd.)

20. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/20 Sample Size Formulas

21. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/21 Coefficient of Variation Researcher may require the sample estimate be within plus or minus G percentage points of the population value Therefore, D = G  The sample size formula may be written as: C coefficient of variation

22. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/22 Stratified Sampling Useful when : The population standard deviation differs by strata The interview cost differs by strata Optimal allocation of sampling budget to various strata: Neyman’s solution where

23. Marketing Research 9th Edition Aaker, Kumar, Day http://www.drvkumar.com/mr9/23 Allocating Sample Size to Strata where