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Research Methods CJ490 Susan Wind

Welcome!

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Sampling

The MOST important part of research process

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Sampling Importance If poor sampling, can’t generalize to a

population Statistical techniques may be used

incorrectly Policy based on research with poor

samples may not be valid

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What is Sampling?

??? ANYONE?

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Sampling is….

Ways to identify a subset of the population that has the same characteristics of the population

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Sampling “Population” Group of elements from which sample is drawn May be based on a concept, such as

Drug Users Domestic Violence Victims

May be specific and have a list Drug uses in a program Victims in a DV shelter

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POPULATION

SAMPLE

5 ELEMENTS

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Sampling Types

Probability Non-Probability

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Probability Sampling Rely on random selection; chance Mathematical formula can identify the

likelihood that a specific element would be selected

Formula can estimate how much the sample will differ from the population

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Non-Probability Sampling Probability of an element being chosen

cannot be determined Often used in social science research Population list is usually not known

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Strengths of Non-Probability Sampling Can be used if no list for population,

which is not uncommon Particularly useful for exploratory

research Also useful for field research

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Weaknesses of Non-Probability Sampling Can’t know if sample accurately

represents the population

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Non-Probability Types Availability Sampling Quota Sampling – accidental sampling

with requirements for a number of respondents in specific group(s)

Purposive or Judgment Sampling Snowball Sampling

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DV victims Survey

You want to study why some women in a shelter for victims of domestic violence return to their batterer.  What kind of non probability sampling will you use?  Explain your answer.

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Availability Sampling Non-probability sampling technique Participants just “happen” to come in contact

with interviewer Interviewer controls the time and place of the

sample, but not who might be available to participate

There is no way of knowing if the sample represents the whole population

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Snowball Sampling

Start with few members Ask those sampled to refer others Excellent for exploratory designs Focus is generally on qualitative

information

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Choosing a Sampling Technique Purpose of study – MOST important factor Scope of study

Large study – Probability sampling is preferred and often “doable”

Small study- depends on other factors Population characteristics:

Extremely important: Is there a list of everyone in the population?

Must have a list to do probability sampling Cost. Convenience

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Questions?

Virtual Office Imail Email Phone if an emergency

Contact information in welcome email and in an announcement

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Research Methods CJ490 Susan WindThanks for

Participating!