Issues in Sampling and Sample Design – A Managerial Perspective CHAPTER 12 Research Methodologies

Introduction The development of sampling theory and the acceptance of sample survey results has made it possible for persons who make decisions to have the ability to collect information quickly and inexpensively and to use that information in their decision making The development of sampling theory and the acceptance of sample survey results has made it possible for persons who make decisions to have the ability to collect information quickly and inexpensively and to use that information in their decision making Service industries such as airlines, hotel/motel chains conduct surveys to learn about their customers and how they can improve their service Service industries such as airlines, hotel/motel chains conduct surveys to learn about their customers and how they can improve their service

Is a Survey Necessary? Surveys are a good way of obtaining accurate information quickly and inexpensively Surveys are a good way of obtaining accurate information quickly and inexpensively In many cases, the information needed may already be available. There is a great deal of information that has been published or is accessible to the public. In many cases, the information needed may already be available. There is a great deal of information that has been published or is accessible to the public. In instances when the information is not available from other sources, a manager should ask whether the data needed is important enough to justify the expense of of conducting a survey to collect it. In instances when the information is not available from other sources, a manager should ask whether the data needed is important enough to justify the expense of of conducting a survey to collect it.

Types of Samples Simple Random Sampling Simple Random Sampling It is a sampling method in which each possible combination of persons/establishments/houses/ or whatever, that exist the area of interest, has the same chance or probability of being selected as every other combination It is a sampling method in which each possible combination of persons/establishments/houses/ or whatever, that exist the area of interest, has the same chance or probability of being selected as every other combination It is one of the purest forms of selecting a sample It is one of the purest forms of selecting a sample

Types of Samples cont… Systematic Sampling Systematic Sampling When only certain combinations are possible When only certain combinations are possible If a sample of two units out of a universe of four (A,B,C,D) was needed, under systematic sampling only combinations of A and C or B and D would be possible If a sample of two units out of a universe of four (A,B,C,D) was needed, under systematic sampling only combinations of A and C or B and D would be possible For the method of sampling to be an acceptable alternative to simple random sampling, the list must be arranged in a nearly random order For the method of sampling to be an acceptable alternative to simple random sampling, the list must be arranged in a nearly random order

Types of Samples cont… Stratified Random Sampling Stratified Random Sampling Stratification means: Stratification means: Separating the universe into small groups of units so that the units within each group have similar characteristics Separating the universe into small groups of units so that the units within each group have similar characteristics Making each of the groups as dissimilar as possible Making each of the groups as dissimilar as possible Placing the units within each group together on a list before selecting the sample Placing the units within each group together on a list before selecting the sample

Types of Sampling cont… Cluster Sampling Cluster Sampling Used to overcome the cost problems of geographic dispersion or to reduce the size of the lisr one needs to develop or work with in selecting a sample Used to overcome the cost problems of geographic dispersion or to reduce the size of the lisr one needs to develop or work with in selecting a sample In cluster sampling, the universe is divided into distinct geographic areas In cluster sampling, the universe is divided into distinct geographic areas

Types of Samples cont… Quota Sampling Quota Sampling This method of sampling requires the enumerators to interview a fixed number of elements with certain characteristics This method of sampling requires the enumerators to interview a fixed number of elements with certain characteristics A quota is established for the number and type of elements to be selected A quota is established for the number and type of elements to be selected It insures that elements with selected characteristics are represented, and, in certain instances, may be the only way that a sample of the population can be drawn It insures that elements with selected characteristics are represented, and, in certain instances, may be the only way that a sample of the population can be drawn

Sampling and Non-sampling Errors There are two basic errors in any sample survey: There are two basic errors in any sample survey: Sampling Error or Standard error – is the variability of the estimates among all possible samples Sampling Error or Standard error – is the variability of the estimates among all possible samples It is associated with the fact that the sample used was only one of the large number of possible same-size samples that could have been selected. Each sample selected would give a different estimate of the characteristics being measured

Sampling and Non-sampling Errors The second type of error is: The second type of error is: Non-sampling Error- there are many possible sources of this error including: Non-sampling Error- there are many possible sources of this error including: Those created by poorly worded questions Those created by poorly worded questions Not obtaining interviews for every sample unit Not obtaining interviews for every sample unit Inadequate coverage of the universe in selecting a sample Inadequate coverage of the universe in selecting a sample Errors made in the processing of data Errors made in the processing of data

Issues to be Considered in Selecting a Sample design The type of information needed The type of information needed The required information is the major factor in making any decisions regarding survey or sample design The required information is the major factor in making any decisions regarding survey or sample design The statistical reliability (or quality) of the data needed. The statistical reliability (or quality) of the data needed. The data needs to be reliable so that a manager can be confident when making a decision The data needs to be reliable so that a manager can be confident when making a decision In deciding on the quality needed form a survey, a manager must keep in mind the purpose for which the data is needed In deciding on the quality needed form a survey, a manager must keep in mind the purpose for which the data is needed

Issues…continued Some surveys are taken so that the results can be used as a promotional tool Some surveys are taken so that the results can be used as a promotional tool Another use made of survey results is for marketing purposes Another use made of survey results is for marketing purposes A third reason for taking a survey is to gather information for general planning or policy making A third reason for taking a survey is to gather information for general planning or policy making

Issues ….continued Once it has been determined what information is needed and what degree of statistical reliability is required, the next step is to: Once it has been determined what information is needed and what degree of statistical reliability is required, the next step is to: Develop an estimate of the resources required to complete the job Develop an estimate of the resources required to complete the job Included as resources are money, staff, and time Included as resources are money, staff, and time

Conclusion Can a manager make do with the information that is available or rely on common sense to come up with the answer being sought? Can a manager make do with the information that is available or rely on common sense to come up with the answer being sought? If the decision is that a survey is necessary, then there are several decisions left to made If the decision is that a survey is necessary, then there are several decisions left to made