#### Transcript Marketing Research Aaker, Kumar, Day Ninth Edition Instructor’s Presentation Slides

Marketing Research Aaker, Kumar, Day Ninth Edition Instructor’s Presentation Slides 1 Chapter Fifteen Sample Size and Statistical Theory Marketing Research 9th Edition Aaker, Kumar, Day 2 http://www.drvkumar.com/mr9/ 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 Marketing Research 9th Edition Aaker, Kumar, Day 3 http://www.drvkumar.com/mr9/ 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 Marketing Research 9th Edition Aaker, Kumar, Day 4 http://www.drvkumar.com/mr9/ 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 Marketing Research 9th Edition Aaker, Kumar, Day 5 http://www.drvkumar.com/mr9/ 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 Marketing Research 9th Edition Aaker, Kumar, Day 6 http://www.drvkumar.com/mr9/ Population Characteristics/ parameters The population opinion on symphony starting time (7:30 P.M. on weekdays) Marketing Research 9th Edition Aaker, Kumar, Day 7 http://www.drvkumar.com/mr9/ Sample Characteristics/Statistics Sample mean ( X ) is used to estimate the unknown population mean Example: A sample of symphony season-ticket holders Marketing Research 9th Edition Aaker, Kumar, Day 8 http://www.drvkumar.com/mr9/ Sample Characteristics/Statistics (contd.) Sample mean Marketing Research 9th Edition Aaker, Kumar, Day 9 http://www.drvkumar.com/mr9/ Sample Reliability X will vary from sample to sample As sample size (n) increases, variation in X will decrease standard error of Marketing Research 9th Edition Aaker, Kumar, Day decreases as the sample size gets larger 10 http://www.drvkumar.com/mr9/ Sampling Distribution Indicates probability of getting a particular sample mean The normal distribution of X Marketing Research 9th Edition Aaker, Kumar, Day 11 http://www.drvkumar.com/mr9/ Sampling Distribution (contd.) The effect of increasing sample size on the normal distribution of X Marketing Research 9th Edition Aaker, Kumar, Day 12 http://www.drvkumar.com/mr9/ Interval Estimation X varies from sample to sample The difference between the sample mean ( X ) 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 Marketing Research 9th Edition Aaker, Kumar, Day 13 http://www.drvkumar.com/mr9/ Interval Estimation Marketing Research 9th Edition Aaker, Kumar, Day 14 http://www.drvkumar.com/mr9/ Interval Estimation (contd.) Size of Interval Estimate depends on: Confidence level Population standard deviation Sample size Marketing Research 9th Edition Aaker, Kumar, Day 15 http://www.drvkumar.com/mr9/ Sample Size Question Size of the sampling error that is desired Confidence level Expected variance Marketing Research 9th Edition Aaker, Kumar, Day 16 http://www.drvkumar.com/mr9/ 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 Marketing Research 9th Edition Aaker, Kumar, Day 17 http://www.drvkumar.com/mr9/ Proportions Population variance, Marketing Research 9th Edition Aaker, Kumar, Day 18 http://www.drvkumar.com/mr9/ Proportions (contd.) Marketing Research 9th Edition Aaker, Kumar, Day 19 http://www.drvkumar.com/mr9/ Sample Size Formulas Marketing Research 9th Edition Aaker, Kumar, Day 20 http://www.drvkumar.com/mr9/ Coefficient of Variation Researcher may require the sample estimate be within plus or minus G percentage points of the population value Therefore, D = Gm The sample size formula may be written as: C Marketing Research 9th Edition Aaker, Kumar, Day coefficient of variation 21 http://www.drvkumar.com/mr9/ 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 Marketing Research 9th Edition Aaker, Kumar, Day 22 http://www.drvkumar.com/mr9/ Allocating Sample Size to Strata where Marketing Research 9th Edition Aaker, Kumar, Day 23 http://www.drvkumar.com/mr9/