Term
sociologists WHAT from a population to discover and understand social phenomena. 

Definition


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Two famous examples of sampling illustrate the importance of proper sampling techniques: 

Definition
1. 1936 Literary Digest presidential poll
2. 1948 Gallup presidential poll 


Term
1936 Literary Digest presidential poll 

Definition
Editors mailed postcards to people in six states, names were selected from telephone directories & automobile registration lists.
Doing so created a sampling frame problem: they only sampled the rich, and therefore did not have an accurate sample to predict the election. 


Term
1948 Gallup presidential poll 

Definition
The Gallup samplers used a method called quota sampling, which selects people to match a set of characteristics (e.g. the poor, those living in rural vs. urban environments).
Predictions were based on old census data: the quotas they used were no longer valid indicators of the U.S. population, and Gallup incorrectly predicted Thomas Dewey defeating Harry Truman 


Term
There are two types of sampling methods: 

Definition
1. Nonprobability sampling 2. Probability sampling 


Term

Definition
represents techniques where samples are not selected by using probability theory. 


Term

Definition
are selected according to some sort of random assignment. 


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There are four types of nonprobability sampling: 

Definition
1. Reliance on available subjects 2. Purposive (or judgmental) sampling 3. Snowball sampling 4. Quota sampling 


Term
Reliance on available subjects (nonprobability sampling) 

Definition
(also called convenience or haphazard sampling) involves using people in close proximity, or people who are gathered in one place at one time.
It is generally considered one of the weaker forms of sampling.
Strengths: easy and efficient Weaknesses: can be unrepresentative of general populations 


Term
Purposive (or judgmental) sampling (nonprobability sampling) 

Definition
units to be observed are selected on the basis of a researcher's judgment about which ones will be most useful or representative.
One may want to interview the entire population of some limited group (e.g. directors of shelters for homeless adults). 


Term
Three guidelines should be followed when selecting a purposive sample: 

Definition
1. Informants should be knowledgeable about the cultural arena, situation, or experience being studied.
2. Informants should be willing to talk.
3. Informants should be representative of the range of points of view. 


Term
In purposive sampling, interviews should be selected until two criteria are met: 

Definition
1. Completeness
2. Saturation 


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Definition
Interviews should continue until a researcher is confident subjects have provided an overall sense of the meaning of a concept, theme, or process. 


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Definition
Interviews should continue until one is confident that they are learning little that is new from subsequent interviews. 


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Definition
a nonprobability sampling method whereby each person interviewed is asked to suggest additional people for interviewing. 


Term
Snowball samples are appropriate for 

Definition
studying difficult to identify or difficult to locate populations 


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Snowball sampling can be problematic for the following reasons: 

Definition
1. It can result in samples with questionable representativeness.
2. Initial contacts may shape the entire sample and foreclose access to some members of the population of interest. 


Term

Definition
is a type of nonprobability sampling in which units are selected into a sample on the basis of prespecified characteristics, so that the total sample will have the same distribution of characteristics assumed to exist in the population being studied. 


Term
Quota sampling begins with 

Definition
a matrix that describes characteristics of a target population. 


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Quota sampling is similar to probability sampling, but has two inherent issues: 

Definition
1. Quota frame problems
2. Selection of sample elements may be biased 


Term

Definition
▪ Proportions that different cells in a matrix represent must be accurate.
▪ It is often difficult to get uptodate information for this purpose. 


Term
Selection of sample elements may be biased. 

Definition
E.g. an interviewer may be instructed to interview 5 people who meet a given set of characteristics, yet still avoid certain people that are representative of the issue at hand. 


Term
In all research designs, sociologists distinguish between WHAT and informants. 

Definition


Term

Definition
allow a researcher to construct a composite picture of the group respondents represent. 


Term

Definition
s are people well versed in a social phenomenon one wishes to study and who are willing to tell what they know about it. 


Term

Definition
is a general term for samples selected in accord with probability theory. 


Term
Probability samples are often used for 

Definition


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Probability sampling can be a very effective tool in research if... 

Definition


Term
Nonprobability sampling cannot 

Definition
guarantee that a sample is representative of a population. 


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Probability sampling is useful 

Definition
because it helps ensure that the same variations that exist in a population are represented in a sample. 


Term

Definition
occurs when subjects selected for a study are not typical nor representative of a larger population. 


Term
Bias is often WHAT. When one selects a sample based on some background characteristic, they ALWAYS introduce some sort of bias into their sample. 

Definition


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Some degrees of bias are more acceptable than others 

Definition
depending on one’s research design 


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Samples must be WHAT of the population from which they are selected 

Definition


Term

Definition
refers to the quality of a sample of having the same distribution of characteristics as the population from which it was selected. 


Term
A sample is representative of the population from which it is selected 

Definition
if all members of the population have an equal chance of being selected in the sample. 


Term
There are two advantages to probability sampling: 

Definition
1. Probability samples are typically more representative than other types of samples because biases are avoided.
2. Probability theory permits researchers to estimate the accuracy or representativeness of a sample. 


Term
In order to understand probability sampling one needs to differentiate WHAT and populations: 

Definition


Term

Definition
A unit of which a population is composed and which is selected in a sample. 


Term

Definition
A specified aggregation of elements in a study. 


Term
In probability sampling, one uses random selection 

Definition
to select a set of elements from a population that accurately portray the total population from which the elements are selected. 


Term
Random selection ensures that each element has an 

Definition
equal chance of selection. 


Term

Definition
provides the basis for estimating parameters of a population. 


Term

Definition
is the summary description of a given variable in a population.
E.g. the mean unemployment rate or age distribution in L.A. are both parameters of the L.A. population. 


Term
When researchers generalize from a sample, they use 

Definition
sample statistics to estimate population parameters. 


Term
An action that involves elements of probability is called an 

Definition
event or trial.
ie ▪ Dealing a card. ▪ Tossing a coin. ▪ Spinning a roulette wheel. 


Term
The result of an event or trial is an 

Definition


Term
An outcome represents the characteristic 

Definition
of the event/trial. For example… ▪ Drawing an ace or a seven or a king, etc. ▪ A coin landing on heads or tails. ▪ A ball landing on double zero (00) in roulette. 


Term
robability is used to predict what kind 

Definition
of samples are likely to be obtained from a population. 


Term
Thus, probability establishes a connection between samples and populations. Inferential statistics rely on this connection when they use 

Definition
sample data as the basis for making conclusions about populations. 


Term

Definition
number of outcomes classifed as A  total number of possible outcomes 


Term
Two conditions must be met for a sample to be random: 

Definition
1. Every individual in a population has an equal chance of being selected.
2. When more than one individual is being selected, the probabilities must stay constant (i.e. there must be sampling with replacement). 


Term
As one selects a bigger sample, 

Definition
the sample mean approaches the population mean. 


Term

Definition
the more accurate its estimation of the population from which it was drawn. 


Term
Although samples can have different means, 

Definition
the sample means should be close to the population mean. 


Term
The sample means (M1 , M2 , M3 …) should cluster around 

Definition


Term
Thus, the distribution of sample means tends to form a normal shape with 

Definition


Term
Any individual sample mean probably will not be identical to its population mean. Therefore, 

Definition
sampling error exists when sampling. 


Term

Definition
represents the degree of error to be expected of a given sample design.
In other words, there is “error” between M and μ.
Some sample means will be relatively close to μ and others will be relatively far away. 


Term
The standard error provides a measure 

Definition
of the standard distance between M and μ. 


Term
The law of large numbers: 

Definition
The larger the sample size (n), the closer the sample means should be to the population mean (μ). 


Term
The formula for standard error reflects the intuitive relationship between 

Definition
standard deviation, sample size, and “error:” 


Term

Definition
standard error decreases. 


Term

Definition
standard error increases. 


Term

Definition
is the estimated probability that a population parameter lies within a given confidence interval. 


Term

Definition
is the range of values within which a population parameter is estimated to lie. 


Term

Definition
is a list of units that compose a population from which a sample is selected. 


Term
If a sample is to be representative of a population, it is essential 

Definition
that the sampling frame include all members of the population. 


Term
There are different ways to sample using probability theory, including… 

Definition
1. Simple random sampling
2. Systematic sampling
3. Stratified sampling 


Term
Simple random sampling is a type 

Definition
of probability sampling in which the units composing a population are assigned numbers. 


Term
Simple random sampling is beneficial in many ways, but it is 

Definition
not necessarily the most accurate sampling method. 


Term
Simple random sampling has 

Definition
A set of random numbers is generated and the units having those numbers are included in the sample. 


Term

Definition
is a type of probability sampling in which every kth unit in a list is selected for inclusion in a sample. 


Term
Generally, systematic sampling is 

Definition
more accurate than simple random sampling. 


Term
Two terms are frequently used in connection with systematic sampling: 

Definition
1. Sampling interval
2. Sampling ratio 


Term

Definition
is the standard distance between elements selected from a population in the sample. 


Term

Definition
is the proportion of elements in a population that are selected to be in a sample. 


Term
Stratified sampling is a modification of 

Definition
either simple random or systematic sampling. 


Term

Definition
refers to the grouping of units composing a population into homogenous groups (strata) before sampling. 


Term
Stratified sampling is slightly more accurate 

Definition
than simple random sampling. 


Term

Definition
is a multistage sampling technique in which natural groups are sampled initially with the members of each selected group being subsampled afterward. 


Term
Cluster sampling is used when it is 

Definition
not practical or possible to create a list of all elements that compose a target population. 


Term
Cluster sampling is efficient, but 

Definition


Term
In multistage cluster sampling, 

Definition
stratification techniques can refine and improve a sample being selected. 


Term
By stratifying a sample in multistage cluster sampling, 

Definition
sampling error can be reduced. 


Term
Probability proportionate to size (PPS) sampling 

Definition
is a type of multistage cluster sample in which clusters are selected not with equal probabilities, but with probabilities proportionate to their sizes—as measured by the number of units to be subsampled. 


Term
PPS is a more sophisticated form of 

Definition


Term
Depending on the nature of one’s population, one may wish to sample a 

Definition
disproportionate amount of one or more elements, or use weighting to sample. 


Term

Definition
assigning different weights to cases that were selected into a sample with different probabilities of selection. 

