SAMPLING FRAME

Sampling design begins by specifying the target population which is the collection of elements or objects that possess the information sought by the researcher and about which inferences are to be made.  

 The target population must be defined precisely that involves translating the problem definition into a precise statement of who should and should not be included in the sample.  For instance, in surveying “hotel guests” about their experiences during their last stay, we may want to include only those guests who can speak and/ or read Hindi.  Such operational definition of the population would be make the scope of the study limited. 

Next, the elements and sampling units themselves must be determined.  An element is an object about which or from which the information is desired.  In a survey research, the element is usually the respondent and a sampling unit is an element or a unit containing the element that is available for selection at some stage of the sampling process.  Is the researcher surveying all hotel guests that fit into the operational definition? 

Sampling Elements :This is the unit about which information is sought by the marketing researcher for further analysis and action.  The most common sampling element is marketing research is a human respondent who could be a consumer, a dealer or a person exposed to an advertisement and so on.  But some other possible elements for a study could be companies, families or households, retail stores and so on. 

Population : This is not the entire population of a given geographical area, but the predefined set of potential respondents (elements) in a geographical area.  For example, a population may be defined as “all mothers who buy branded baby food in a given area” or “all teenagers who watch MTV in the country” or “all adult males who have heard about or use the AQUAFRESH brand of toothpaste” or similar definitions in line with the study being done. 

Sampling Frame: The list from which the respondents are drawn is referred to as the sampling frame which includes available or constructed lists obtained from different sources specifically for the purposes of the study.  Membership, Directories, or customer lists even invoices or credit card receipts can be used as a sampling frame. Factors like comprehensiveness, accuracy, currency, and duplication must be taken into account at the time of determining potential sampling frame errors. Even though it is a relatively easy task to define a target population for a study, it is much more difficult to identity or lists every member of such a population.  In most cases, therefore, we decide on a sampling frame, a subset of the defined target population, from which we can select a sample for our research.  For example, we may use a telephone directory of Mumbai as a sampling frame to represent the target population.  Evidently, there would be a number of people) who fit our population definition, but do not figure in the telephone directory.  Similarly, some who have moved out of Mumbai recently would still be listed.  Thus, a sampling frame is usually a practical listing of the population or a definition of the elements or areas which can be used for the sampling exercise.  For reasons of budget or time constraints, certain areas of the country may be excluded from the sampling frame of a study, even though they would be a part of the defined population. 

Sampling Unit :If individual respondents form the sample elements, and if we directly select some individuals in a single step, the sampling unit is also the elements. That is, both the units and the element are the same.  But in most marketing research, there is a multi- stage selection.  For example, we may first select areas or blocks in a city or town.  These form the first stage-sampling units.  Then we may select apartments or houses – the third state sampling units.  At the last stage, we reach the individual sampling element – the respondent we wanted to meet.