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67 Cards in this Set
- Front
- Back
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Sample
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A subset, or some part, of a larger population
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Population (universe)
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Any complete group of entities that share some common set of characteristics
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Population Element
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An individual member of a population
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Census
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An investigation of all the individual elements that make up a population
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Sampling Frame
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A list of element from which a sample may be drawn; also called working population
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Sampling Frame
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A list of elements from which a sample may be drawn; also called working population
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Reverse directory
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A directory similar to a telephone directory except that listings are by city and street address or by phone number rather than alphabetical by last name
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Sampling Frame Error
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An error that occurs when certain sample elements are not listed or are not accurately represented in a sampling frame
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Sampling Unit
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A single element or group of elements subject to selection in he sample
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Primary Sampling Unit (PSU)
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A term used to designate a unit selected in the first stage of sampling
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Secondary Sampling Unit
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A term used to designate a unit selected in the second stage of sampling
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Tertiary Sampling Unit
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A term used to designate a unit selected in the third stage of sampling
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Random Sampling Error
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The difference between the sample result and the result of a census conducted using identical procedures
A function of Sample Size The laws of probability make it possible to estimate the size of RSE |
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Probability Sampling
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A sampling technique in which every member of the population has a known, nonzero probability of selection
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Nonprobability Sampling
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A sampling technique in which units of the sample are selected on the basis of personal judgement or convenience; the probability of any particular member of the population being chosen is unknown
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Convenience Sampling
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The sampling procedure of obtaining those people or units that are most conveniently avaliable
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Judgement (purposive) Sampling
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A nonprobability sampling technique in which an expereicned individual selects the sa,ple based on personal judgement about some appropriate characteristic of the sample member
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Quota Sampling
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A nonprobability sampling procedure that ensures that various subgroups or a population will be represented on pertinent characeristics to the exact extent that the investigator desires
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Snowball Sampling
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A sampling proceudre in which initial respondents are selected by probability methods and additional respondents are obtained from information provided by the initial respondents
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Simple Random Sampling
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A sampling procedure that assures each element in the population of an equal chance of being included in the sample
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Systematic Sampling
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A sampling procedure in which a starting point is selected by a random process and then every 'n'-th number on the list is selected
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Stratified Sampling
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A probabiliy sampling procedure in which simple random subsamples that are more or less equal on some characteristic are drawn from within each stratum of the population
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Proportional Stratified Sample
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A stratified sample in which the number of sampling units drawn from each stratum is in proportion to the population size of that stratum
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Disproportional Stratified Sample
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A stratified sample in which the sample size for each stratum is allocated according to analytical considerations
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Cluster Sampling
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An economically efficient sampling technique in which the primary sampling unit is not the individual element in the popluation but a large cluster of elements; clusters are selected randomly
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Multistage Area Sampling
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Sampling that involves using a combination of two or more probability sampling techniques
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What is the everyday purpose of Sampling?
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Saily life is full of sampling behaviour -- not scientific but illustrative of hte purpose of sampling
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Scientific Reasons for Sampling
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1) Practicality - saves time, cost and labour
2) Sufficiency - can provide acceptable accuracy and reliability 3) Conservation |
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Universe
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Complete of elements sharing a common set of characteristics
*A universe is infinite (unbounded) |
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Census
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An investigation of all the individual members of a population; each and every population element is examined
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Mailing List
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List of names, addresses, and phone numbers of specific populations; generally avaliable from list brokers (commercial vendors) who obtain lists of ournal subscribers
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Reverse Dictionary
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Lists population elements by street addres of phone number rather than alphabetically by name of subscriber
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Sampling Frame Error
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Results when (1) certain sample elements are excluded, or (2) the entire population is not accurately represented
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Sampling Unit
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A single population element or a group of elements subect to selection in the sample
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Stages in Sample Selection
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1) Defining the Target Population
2) Selecting a Sampling Frame 3) Deciding on a probability or nonporbability sample 4) Planning the sampling procedure 5) Determining Sample Size 6) Selecting the actual sampling units 7) Conducting Field Work |
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Defining the Target Population
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Not always obvious ust waht the target population is; errors are possible if this issue isn't carefully thought through -- requires identifying the appropriate sampling units
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Selecting a Sampling Frame
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What are the elements in the target population you can actually access?
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Deciding on a Probability or Nonprobability Sample
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Depends on the nature of the research issues
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Planning the Sampling Procedure
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Depends on the choice of probability or nonprobability sampling
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Determining Sample Size
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In the case of a probability sample this is a statistical proces based on an estimate of the variance, the acceptable error, and the desired confidence level; in the case of nonprobability samples, largely a matter of judgement
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Selecting the Actual Sampling Units
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Regquries taking into account sources of error that can confound the research study
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Conducting Fieldwork
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Has to do with various issues involved in actually collecting data -- procedures for dealing with nonresponses, refusals, callbacks and so on
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Nonprobability Sampling
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Units of the sample are selected on the basis of personal udgement or convenience
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Consequences of chooing a Nonprobability Sample
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1) The chance of any particular member of the target population being chosen is unknown
2) There is no way of measuring random samling error in a nonprobability sample |
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Convenience Sampling
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Used to obtain the most conveniently avaliable sample units
* Gets a large Sample quickly and economically * Best used for exploratory research * Not representative of anything other than the specific sample you obtain |
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Judgement (Purposive) Sampling
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An experience individual selects the sample based on some requried or appropriate characteristics of the sample units
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Quota Sampling
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Ensures that certain characteristics of the target population will be represented in the sample: (1) in proportion to their representation in the population, or (2) according to characteristics required by the researcher
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Snowballing Sampling
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Useful when the target population is unique in some way and no lists are avaliable. Initial sample units are selelcted on a probability basis. Those persons are then solicited for the names of additional similar respondents wtih whom they are acquainted
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Advantages of Probability Sampling
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1) Every member of the target population has a known, nonzero chance of being selected in the sample
2) It is therefore possible to statistically determine the likely zie of random sampling error by specifying a confidence interval within which the population parameter is likely to fal |
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Simple Random Sampling
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Each element in the population has an equal chance of being included in the sample
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Systematic Sampling
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An initial starting point in a list is selected randomly and then every nth item in the list is selected for the sample
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Sampling Interval
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The number of population Units between units selected for the sample
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Periodicity
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A possible problem in systematic sampling if the list has a repetitive pattern
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Stratified Sampling
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Simple random subsamples are drawn from within different population strata are more or less equal in some characteristic
More efficient than a simple random sample More accurately reflects the overall target population |
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Homogeneity and Heterogenety in Stratified Sampling
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The basis chosen for stratification should increase homogenity within each stratum and increase heterogeneity between strata
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Proportional Stratified Sampling
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The number of sampling units within each stratum is in proportion to the relative size of that stratum in the population
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Disproportional Stratified Sampling
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When there exists some significant dsiparity among sampling units it makes more sense to sample different kinds of units disporoportionately
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Cluster Sampling
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An economically efficient sampling technique used when population elements are geographically widespread. The primary sampling unit (PSU) is not an individual element, but a cluster of elements. Secondary sampling (SSUs) of smaller segments may also be selected
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Area Sample
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A cluster sample in which the PSU is a geogrpahical area
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Multistage Area Sampling
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Using a combination of probability sampling techniques -- typically progressively smaller geographical areas randomly selected
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Sample Design Considerations
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Each of the various sampling techniques has advantages and disadvantages
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Internet Sampling
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The internet provides some unique opportunities as well as some unique problems in sampling
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Advantages of Internet Sampling
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The main advantages is speed -- huge samples or samples of specialized nature can be collected quickly and economically
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Disadvantages of Internet Sampling
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Inaccurate Representation
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Internet Sampling: Panel Samples
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It is possible to draw random consumer panels from among Internet uses who have agreed to participate
*May involve use of some incentie such as sweepstakes, cash or points *Main advantage is the use of a database of persons who have provided demographic information on product warrant registration |
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Internet Sampling: Propensity Weighting
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A procedure based on correction factors derived from comparisons made between parallel samples obtained from regular mail and Internet survey results
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Internet Sampling: Opt-in Lists
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Databases comprised of persons who have given permission to be contacted by email
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