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SAMPLE AND SAMPLING TERMINOLOGY:Saves Cost, Labor, and Time

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Research Methods ­STA630
VU
Lesson 26
SAMPLE AND SAMPLING TERMINOLOGY
A sample is a subset, or some part, of a larger whole. A larger whole could be anything out which
sample is taken. That `whole' could be a bucket of water, a bag of sugar, a group of organizations, a
group of students, a group of customers, or a group mid-level managers in an organization. A complete
group of entities sharing some common set of characteristics is population. In other words, the totality
out of which sample is drawn is referred to as population.
Why sample?
1. Saves Cost, Labor, and Time
Applied research projects usually have budget and time constraints. Since sample can save financial cost
as well as time, therefore, to go for sample study is pragmatic.
Of course, a researcher investigating a population with an extremely small number of population
elements may elect to conduct a study on the total population rather than a sample because cost, labor,
and time constraints are relatively insignificant.
Although sample study cuts costs, reduces labor requirements, and gathers vital information quickly, yet
there could be other reasons.
2. Quality Management/supervision
Professional fieldworkers are a scarce commodity. In a large study rather than employing less qualified
staff it may be advisable to do a sample study and employ highly qualified professional fieldworkers. It
can certainly affect the quality of the study. At the same time it may be easier to manage a small group
and produce quality information. Supervision, record keeping, training, and so forth would all be more
difficult in a very large study.
3. Accurate and Reliable Results
Another major reason for sampling is that samples, if properly selected, are sufficiently accurate in most
of the cases. If the elements of a population are quite similar, only a small sample is necessary to
accurately portray the characteristics of interest. Most of us have had blood samples taken from the
finger, the arm, or another part of body. The assumption is that blood is sufficiently similar through out
the body, the characteristics of the blood can be determined on the basis of sample.
When the elements of population are highly homogenous, samples are highly representative of the
population. Under these circumstances almost any sample is as good as another.
Samples may be more accurate than census. In a census study of large population there is a greater
likelihood of non-sampling errors. In a survey mistakes may occur that are unrelated to the selection of
people in the study. For example, a response may be coded incorrectly, or the keyboard operator might
make data entry error. Interviewer mistakes, tabulation errors, and other non-sampling errors may
increase during census because of the increased volume of work. In sample increased accuracy is
possible because the fieldwork and tabulation of the data can be closely supervised than would be
possible in a census. In field survey, a small, well trained, closely supervised group may do a more
careful and accurate job of collecting information than a large group of nonprofessional interviewers
trying to contact everyone.
4. Sampling may be the Only Way
Many research projects, especially those in quality control testing, require the destruction of the items
being tested. If the manufacturer of firecrackers wished to find out whether each product met a specific
production standard, there would be no product left after testing. Similarly, consider the case of electric
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Research Methods ­STA630
VU
bulbs. In testing the life of bulbs, if we were to burn every bulb produced, there would be none left to
sell. This is destructive sampling.
5. Determine the Period of Study
Interviewing every element of a large population without sampling requires lot of time, may be a year or
more. In such a long period study, even the seasonal variation may influence the response pattern of the
respondents. For example, if the study was aimed at measuring the level of unemployment in a given
large city, the unemployment rate produced by the survey data would not refer to the city as of the
beginning of interviewing or as of the end. Researcher may be forced to attribute the unemployment to
some hypothetical date, representing to the midpoint of the study period. Hence it will be difficult to
determine the exact timing to which the data of the study pertains.
Sampling Terminology
There are a number of technical terms used in books on research and statistics which need explanation.
Some of the important terms are:
Element
An element is that unit about which information is collected and which provides the basis of analysis.
Typically, in survey research, elements are people or certain types of people. It is that unit about which
information is collected and that provides the basis of analysis. It can be a person, groups, families,
organizations, corporations, communities, and so forth.
Population
A population is the theoretically specified aggregation of study elements. It is translating the abstract
concept into workable concept.  For example, let us look at the study of "college students."
Theoretically who are the college students? They might include students registered in government
colleges and/or private colleges, students of intermediate classes and/or graduate classes, students of
professional colleges and/or non-professional colleges, and many other variations. In this way the pool
of all available elements is population.
Target Population
Out of the conceptual variations what exactly the researcher wants to focus on. This may also be called
a target population. Target population is the complete group of specific population elements relevant to
the research project. Target population may also be called survey population i.e. that aggregation of
elements from which the survey sample is actually selected.
At the outset of the sampling process, it is vitally important to carefully define the target population so
the proper source from which the data are to collected can be identified. In our example of `college
students" finally we may decide to study the college students from government institutions located in
Lahore, who are studying social sciences, who are aged 19 years of age, and hailing from rural areas.
Sampling
The process of using a small number of items or parts of a larger population to make conclusions about
the whole population. It enables the researchers to estimate unknown characteristics of the population.
Sampling Frame
In actual practice the sample will be drawn from a list of population elements that is often different from
the target population that has been defined. A sampling frame is the list of elements from which the
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Research Methods ­STA630
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sample may be drawn. A simple example could be listing of all college students meeting the criteria of
target population and who are enrolled on the specified date.
A sampling frame is also called the working population because it provides the list that can be worked
with operationally. In our example, such a list could be prepared with help of the staff of the selected
colleges.
Sampling Frame Error
A sampling frame error occurs when certain sample elements are excluded or when the entire
population is not accurately represented in the sampling frame. The error that occurs when certain
sample elements are not listed or available and are not represented in the sampling frame.
Sampling Unit
A sampling unit is that element or set of elements considered for selection in some stage of sampling.
Sampling may be done in single stage or in multiple stages. In a simple, single-stage sample, the
sampling units are the same as the elements. In more complex samples, however, different levels of
sampling units may be employed. For example, a researcher may select a sample of Mohallahs in a
city, and then select a sample of households from the selected Mohallahs, and finally may select a
sample of adults from the selected households. The sampling units of these three stages of sampling are
respectively Mohallah, households, and adults, of which thee last of these are the elements. More
specifically, the terms "primary sampling units," "secondary sampling units," and "final sampling units"
would be used to designate the successive stages.
Observation Unit
An observation unit, or unit of data collection, is an element or aggregation of elements from which the
information is collected. Often the unit of analysis and unit of observation are the same ­ the individual
person ­ but this need not be the case. Thus the researcher may interview heads of household (the
observation units) to collect information about every member of the household (the unit of analysis).
Parameter
A parameter is the summary description of a given variable in a population. The mean income of all
families in a city and thee age distribution of the city's population are parameters. An important part
portion of survey research involves the estimation of population parameters on the basis of sample
observation.
Statistic
A statistic is the summary description of a given variable in a survey sample. Thus the mean income
computed from the survey sample and the age distribution of that sample are statistics. Sample statistics
are used to make estimates of the population parameters.
Sampling Error
Probability sampling methods seldom, if ever, provide statistics exactly equal to the parameters that they
are used to estimate. Probability theory, however, permits us to estimate the error to be expected for a
given sample (more information to be sought from professional in Statistics).
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Table of Contents:
  1. INTRODUCTION, DEFINITION & VALUE OF RESEARCH
  2. SCIENTIFIC METHOD OF RESEARCH & ITS SPECIAL FEATURES
  3. CLASSIFICATION OF RESEARCH:Goals of Exploratory Research
  4. THEORY AND RESEARCH:Concepts, Propositions, Role of Theory
  5. CONCEPTS:Concepts are an Abstraction of Reality, Sources of Concepts
  6. VARIABLES AND TYPES OF VARIABLES:Moderating Variables
  7. HYPOTHESIS TESTING & CHARACTERISTICS:Correlational hypotheses
  8. REVIEW OF LITERATURE:Where to find the Research Literature
  9. CONDUCTING A SYSTEMATIC LITERATURE REVIEW:Write the Review
  10. THEORETICAL FRAMEWORK:Make an inventory of variables
  11. PROBLEM DEFINITION AND RESEARCH PROPOSAL:Problem Definition
  12. THE RESEARCH PROCESS:Broad Problem Area, Theoretical Framework
  13. ETHICAL ISSUES IN RESEARCH:Ethical Treatment of Participants
  14. ETHICAL ISSUES IN RESEARCH (Cont):Debriefing, Rights to Privacy
  15. MEASUREMENT OF CONCEPTS:Conceptualization
  16. MEASUREMENT OF CONCEPTS (CONTINUED):Operationalization
  17. MEASUREMENT OF CONCEPTS (CONTINUED):Scales and Indexes
  18. CRITERIA FOR GOOD MEASUREMENT:Convergent Validity
  19. RESEARCH DESIGN:Purpose of the Study, Steps in Conducting a Survey
  20. SURVEY RESEARCH:CHOOSING A COMMUNICATION MEDIA
  21. INTERCEPT INTERVIEWS IN MALLS AND OTHER HIGH-TRAFFIC AREAS
  22. SELF ADMINISTERED QUESTIONNAIRES (CONTINUED):Interesting Questions
  23. TOOLS FOR DATA COLLECTION:Guidelines for Questionnaire Design
  24. PILOT TESTING OF THE QUESTIONNAIRE:Discovering errors in the instrument
  25. INTERVIEWING:The Role of the Interviewer, Terminating the Interview
  26. SAMPLE AND SAMPLING TERMINOLOGY:Saves Cost, Labor, and Time
  27. PROBABILITY AND NON-PROBABILITY SAMPLING:Convenience Sampling
  28. TYPES OF PROBABILITY SAMPLING:Systematic Random Sample
  29. DATA ANALYSIS:Information, Editing, Editing for Consistency
  30. DATA TRANSFROMATION:Indexes and Scales, Scoring and Score Index
  31. DATA PRESENTATION:Bivariate Tables, Constructing Percentage Tables
  32. THE PARTS OF THE TABLE:Reading a percentage Table
  33. EXPERIMENTAL RESEARCH:The Language of Experiments
  34. EXPERIMENTAL RESEARCH (Cont.):True Experimental Designs
  35. EXPERIMENTAL RESEARCH (Cont.):Validity in Experiments
  36. NON-REACTIVE RESEARCH:Recording and Documentation
  37. USE OF SECONDARY DATA:Advantages, Disadvantages, Secondary Survey Data
  38. OBSERVATION STUDIES/FIELD RESEARCH:Logic of Field Research
  39. OBSERVATION STUDIES (Contd.):Ethical Dilemmas of Field research
  40. HISTORICAL COMPARATIVE RESEARCH:Similarities to Field Research
  41. HISTORICAL-COMPARATIVE RESEARCH (Contd.):Locating Evidence
  42. FOCUS GROUP DISCUSSION:The Purpose of FGD, Formal Focus Groups
  43. FOCUS GROUP DISCUSSION (Contd.):Uses of Focus Group Discussions
  44. REPORT WRITING:Conclusions and recommendations, Appended Parts
  45. REFERENCING:Book by a single author, Edited book, Doctoral Dissertation