Sampling
The objective of most marketing research projects is to obtain information about the characteristics or parameters of a population. Such information may be obtained by taking either a census or sample. Budget and time limits, large population size, and small variance in the characteristic of interest most often favor the use of a sample. How is sampling performed?
The sampling design process includes five steps which are closely interrelated and relevant to all aspects of the marketing research project, from problem definition to the presentation of the results. These five steps are: defining the target population; determining the sample frame; selecting a sampling technique; determining the sample size; and executing the sampling process. Let us look at each of these more closely.
1. Defining the Target Population: The target population is the collection of elements or objects that possess the information sought by the researcher, and about which inferences are to be made
2. Determining the Sample Frame: A sample frame is a representation of the elements of the target population
3. Selecting a Sampling Technique: Selecting a sampling technique involves several decisions, such as whether to use a Bayesian or traditional sampling approach, sample with or without replacement, and use nonprobability or probability sampling
4. Determining the Sample Size: Determining the sample size involves several qualitative and quantitative considerations, such as the importance of the decision; the nature of the research; the number of variables involved; the costs involved in execution; the nature of the analysis, completion rates, statistical power, and confidence intervals
5. Executing the Sampling Process: Execution of the sampling process requires a detailed specification of how the sampling decisions are to be implemented with respect to the population; sampling frame; sampling unit; sampling technique; and sample size
Data Collection
Marketing researchers often use questionnaires to obtain quantitative primary data. A questionnaire is a set of questions, which are very carefully and purposely designed to capture as much of the information necessary for addressing the research question(s) and for minimizing response error.
Regardless of form (for example, questionnaire, structured interview, and so forth), researchers have two major options for collecting data: developing their own organizations, or contracting with field-work agencies. In either case, data collection involves the use of a field force. In projects demanding direct contact between field workers and respondents, all field workers should be trained in important aspects of the data collection process, including making the initial contact; asking the questions; probing; recording the answers; and terminating the interview. Supervision of field workers involves quality control and editing; sampling control; checks for cheating; central office control; and validity and reliability measures.
Data Preparation
The data must be prepared before any analysis can be performed. Data preparation is a meticulous process. Each questionnaire must be checked for completeness and accuracy. Incomplete, ambiguous, and inconsistent responses cannot be utilized in the analysis. The data must be coded; that is, a numeric or alphanumeric code is assigned to specific responses to each specific question. The coded data is then entered into a computer system and further treated for missing values. Options available for treating missing responses include substitution of a neutral value, such as the arithmetic mean; substitution of an imputed response; casewise deletion; and pairwise deletion. Data can also be statistically adjusted in an effort to enhance the quality of data analysis. Adjustment procedures include weighting, variable respecification, and scale transformations.
