Selecting research participant
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Selecting Research Participant. Sample & Population. A population is the entire set of individuals of interest to a researcher. A sample is a set of individuals selected from a population and usually is intended to represent the population in a research study. Selection bias.

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Selecting Research Participant

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Selecting research participant

Selecting Research Participant


Sample population

Sample & Population

  • A population is the entire set of individuals of interest to a researcher.

  • A sample is a set of individuals selected from a population and usually is intended to represent the population in a research study.


Selection bias

Selection bias

  • A representative sample is a sample with the same characteristics as the population.

  • A biased sample is a sample with different characteristics from those of the population.

  • Selection bias or sampling bias occurs when participants or subjects are selected in a manner that increases the probability of obtaining a biased sample.


Sample size

Sample Size

The first principle is that a large sample is probably more representative than a small sample.

Although large samples are good, there is also a practical limit to the number of individuals that is reasonable to use in a research study.


Sample size1

Sample Size

  • Although a sample size of 25 or 30 individuals for each group or each treatment condition is a good target, other considerations may make this sample size unreasonably large or small.

  • It can be computed that for a population of 100,000 or more the sample must have at least 384 individuals to be confident that the preferences observed in the sample are within 5% of the corresponding population preferences.


Sampling basics

Sampling Basics

  • Sampling methods fall into two basic categories:

  • probability sampling (5 types)

  • nonprobability sampling.(2 types)


Selecting research participant

33%White

33%Black

33%Latino

60% White,

10% Black,

30% Latino


Selecting research participant

Random schools

33% available White

33% available Black

33% available Latino


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