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

2. Sample Size and Statistical Theory
Chapter Fifteen
Sample Size and Statistical Theory
Marketing Research 9th Edition
Aaker, Kumar, Day

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
Marketing Research 9th Edition
Aaker, Kumar, Day

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
Marketing Research 9th Edition
Aaker, Kumar, Day

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
Marketing Research 9th Edition
Aaker, Kumar, Day

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
Marketing Research 9th Edition
Aaker, Kumar, Day

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

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

9. Sample Characteristics/Statistics (contd.)
Sample mean
Marketing Research 9th Edition
Aaker, Kumar, Day

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
Marketing Research 9th Edition
Aaker, Kumar, Day

11. Sampling Distribution
Indicates probability of getting a particular sample mean
The normal distribution of
Marketing Research 9th Edition
Aaker, Kumar, Day

12. Sampling Distribution (contd.)
The effect of increasing sample size on the normal distribution of
Marketing Research 9th Edition
Aaker, Kumar, Day

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
Marketing Research 9th Edition
Aaker, Kumar, Day

14. Interval Estimation Marketing Research 9th Edition Aaker, Kumar, Day

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

16. Sample Size Question Size of the sampling error that is desired
Confidence level
Expected variance
Marketing Research 9th Edition
Aaker, Kumar, Day

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
Marketing Research 9th Edition
Aaker, Kumar, Day

18. Proportions Population variance, Marketing Research 9th Edition
Aaker, Kumar, Day

19. Proportions (contd.) Marketing Research 9th Edition Aaker, Kumar, Day

20. Sample Size Formulas Marketing Research 9th Edition Aaker, Kumar, Day

21. 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 coefficient of variation
Marketing Research 9th Edition
Aaker, Kumar, Day

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
Marketing Research 9th Edition
Aaker, Kumar, Day

23. Allocating Sample Size to Strata
where
Marketing Research 9th Edition
Aaker, Kumar, Day