ENVI 498 Lecture Notes - Lecture 10: Complete Group, Central Tendency, Stratified Sampling
Population (Universe)
Any complete group of entities
Accurate and Reliable Results
Samples can yield REASONABLY ACCURATE information.
Strong similarities in population elements make sampling possible.
Destruction of Test Units
Sampling reduces the COSTS of research in finite populations.
The SAMPLING FRAME
A list of elements from which a sample may be drawn; also called working population.
Sampling Unit
A single element or group of elements subject to selection in the sample.
PSU
Primary Sampling Unit (selected in the first stage of sampling
Random Sampling Error
- The difference between the sample result and the result of a census conducted using identical
procedures
- A statistical fluctuation that occurs because of chance variations in the elements selected for a sample.
fac
Systematic Sampling Error
Systematic (non-sampling) error results from non sampling factors, primarily the nature of a study's
design and the correctness of the execution.
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Probability Sampling
A sampling technique in which every member of the population has a known, nonzero probability of
selection.
Non-probability Sampling
A sampling technique in which units of the sample are selected on the basis of personal judgement or
convenience.
Probability of any one member of the population being chosen is unknown.
Convenience Sampling
(NonProb Sampling)
Obtaining those people or units that are most conveniently available.
Judgement (Purposive) Sampling
(NonProb Sampling)
An experienced individual selects the sample based on personal judgement about some appropriate
characteristic of the sample member.
Quota Sampling
(NonProb Sampling)
Ensures that various subgroups of a population will be represented on pertinent characteristics to the
exact extent that the investigator desires.
Advantages: Speed of data collection, lower costs, CONVENIENCE.
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Sources of Bias for Non probability Sampling
Respondents chosen because they were:
- similar to interviewer
- easily found
- willing to be interviewed
- middle-class
Snowball Sampling
(NonProb Sampling)
A sampling procedure in which initial respondents are selected by probability methods and additional
respondents are obtained from information provided by the initial respondents.
Simple Random Sampling
Assures each element in the population of an equal chance of being included in the sample.
Systematic Sampling
A starting point is selected by a random process and then every nth number on the list is selected.
Stratified Sampling
Simple random subsamples that are more or less equal on some characteristic are drawn from within
each stratum of the population.
Proportional Stratified Sample
The number of sampling units drawn from each stratum is in proportion to the population size of that
stratum.
Disproportional Stratified Sample
The sample size of each stratum is allocated according to analytical considerations.
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Document Summary
Strong similarities in population elements make sampling possible. Sampling reduces the costs of research in finite populations. A list of elements from which a sample may be drawn; also called working population. A single element or group of elements subject to selection in the sample. Primary sampling unit (selected in the first stage of sampling. The difference between the sample result and the result of a census conducted using identical procedures. A statistical fluctuation that occurs because of chance variations in the elements selected for a sample. fac. Systematic (non-sampling) error results from non sampling factors, primarily the nature of a study"s design and the correctness of the execution. A sampling technique in which every member of the population has a known, nonzero probability of selection. A sampling technique in which units of the sample are selected on the basis of personal judgement or convenience. Probability of any one member of the population being chosen is unknown.
