Lecture Marketing research (12th edition) - Chapter 14: Sampling fundamentals

Chapter 14 - Sampling fundamentals. In this chapter, the following content will be discussed: Sampling fundamentals, error in sampling, sampling process, sampling techniques, types of stratified sampling, inversely proportional stratified sampling,...

1 Marketing Research Aaker, Kumar,  Leone and Day  Twelfth Edition Instructor’s  2 Chapter Fourteen Sampling Fundamentals Marketing Research 12th Edition 3 Sampling Fundamentals When is census appropriate? • • • • Population size is quite small Information is needed from every individual in  the population Cost of making an incorrect decision is high  Sampling errors are high Marketing Research 12th Edition 4 Sampling Fundamentals (Contd.) When is sample appropriate?  • • • • • • Population size is large Both cost and time associated with obtaining information  from the population is high Quick decision is needed To increase response quality since more time can be spent  on each interview Population being dealt with is homogeneous If census is impossible Marketing Research 12th Edition 5 Error in Sampling Total Error ▫ Difference between the true value and the observed  value of a variable • Sampling Error ▫ Error is due to sampling • Non­sampling Error ▫ Error is observed in both census and sample Marketing Research 12th Edition 6 Error in Sampling (contd.) Marketing Research 12th Edition 7 Sampling Process Determining Target Population • • • • • • • Well thought out research objectives  Consider all alternatives Know your market Consider the appropriate sampling unit Specify clearly what is excluded Should be reproducible Consider convenience Marketing Research 12th Edition 8 Sampling Process (Contd.) Determining Sampling Frame • • List of population members used to obtain a sample Issues: ▫ Obtaining appropriate lists ▫ Dealing with population sampling frame differences  Superset problem  Intersection problem Selecting a Sampling Procedure • • Choose between Bayesian and Traditional sampling  procedure Decide whether to sample with or without replacement Marketing Research 12th Edition 9 The Sampling Process Marketing Research 12th Edition 10 10 Sampling Techniques Marketing Research 12th Edition 12 12 Directly Proportional Stratified Sampling Marketing Research 12th Edition 13 13 Inversely Proportional Stratified Sampling q q q Assume that among the 600 consumers in the population, 200 are heavy  drinkers and 400 are light drinkers.   If a research values the opinion of the heavy drinkers more than that of the  light drinkers, more people will have to be sampled from the heavy  drinkers group.  If a sample size of 60 is desired, a 10 percent inversely proportional  stratified sampling is employed The selection probabilities are computed as follows: Denominator 600/200 + 600/400 = + 1.5 = 4.5 Heavy Drinkers proportional and sample size 3/ 4.5 = 0.667; 0.667 * 60 = 40 Light drinkers proportional and sample size 1.5 / 4.5 = 0.333; 0.333 * 60 = 20 Marketing Research 12th Edition 14 14 Cluster Sampling • • • • Involves dividing population into subgroups  Random sample of subgroups/clusters is  selected and all members of subgroups are  interviewed  Very cost effective Useful when subgroups can be identified that  are representative of entire population Marketing Research 12th Edition 15 Comparison of Stratified & Cluster Sampling Processes Stratified sampling Cluster sampling Homogeneity within group Homogeneity between groups Heterogeneity between groups Heterogeneity within groups All groups are included Random selection of groups Sampling efficiency improved by Sampling efficiency improved by decreasing cost at a faster rate than increasing accuracy at a faster rate than accuracy cost Marketing Research 12th Edition 16 16 Systematic Sampling • • • Involves systematically spreading the sample  through the list of population members Commonly used in telephone surveys Sampling efficiency depends on ordering of the  list in the sampling frame Marketing Research 12th Edition 17 17 Non Probability Sampling • • Costs and trouble of developing sampling  frame are eliminated Results can contain hidden biases and  uncertainties Used in: • • • • •   The exploratory stages of a research project   Pre­testing a questionnaire   Dealing with a homogeneous population   When a researcher lacks statistical knowledge   When operational ease is required Marketing Research 12th Edition 18 18 Types of Non Probability Sampling Marketing Research 12th Edition 19 19 Quota Sampling ­ Example Marketing Research 12th Edition 20 20 Non­Response Problems • Respondents may: ▫ ▫ ▫ • • • Refuse to respond Lack the ability to respond Be inaccessible Sample size has to be large enough to allow for non  response Those who respond may differ from non respondents in  a meaningful way, creating biases Seriousness of non­response bias depends on extent of  non response Marketing Research 12th Edition 21 21 Solutions to Non­response Problem • • • Improve research design to reduce the  number of non­responses Repeat the contact one or more times (call  back) to try to reduce non­responses Attempt to estimate the non­response bias Marketing Research 12th Edition 22 22 Shopping Center Sampling • • 20% of all questionnaires completed or  interviews granted are store­intercept  interviews Bias is introduced by methods used to select Marketing Research 12th Edition 23 23 Shopping Center Sampling (Contd.) Solutions to Bias • Shopping Center Bias ▫ ▫ • Use several shopping centers in different neighborhoods Use several diverse cities Sample Locations Within a Center ▫ ▫ ▫ Stratify by entrance location Take separate sample from each entrance To obtain overall average, strata averages should be combined by  weighing them to reflect traffic that is associated with each  entrance Marketing Research 12th Edition 24 24 Solutions to Bias (contd.) • Time Sampling ▫ Stratify by time segments ▫ Interview during each segment ▫ Final counts should be weighed according to traffic  counts • Sampling People versus Shopping Visits –  Options: ▫ Ask respondents how many times they visited the  shopping center during a specified time period,  such as the last four weeks and weight results  according to frequency Marketing Research 12th Edition 25 25 Different Levels of Sampling  Frames Marketing Research 12th Edition 26 End of Chapter Fourteen Marketing Research 12th Edition ... Decide whether to sample with or without replacement Marketing Research 12th Edition 9 The Sampling Process Marketing Research 12th Edition 10 10 Sampling Techniques Marketing Research 12th Edition 11 11 Types of Stratified Sampling Proportionate Stratified Sampling ... according to frequency Marketing Research 12th Edition 25 25 Different Levels of Sampling Frames Marketing Research 12th Edition 26 End of Chapter Fourteen Marketing Research 12th Edition ...2 Chapter Fourteen Sampling Fundamentals Marketing Research 12th Edition 3 Sampling Fundamentals When is census appropriate? • • • • Population size is quite small