Transcript Chapter 6 - People Server at UNCW

Chapter 6
Selecting Research
Participants
Selecting research participants

In research you select a sample from a
population of potential participants.

Census – the whole population is researched

Inferential statistics – used to make
statements (inferences) about the population
based on the findings from our sample.

Sampling frame – a list of the population from
which the sample is drawn.
Sampling methods

Probability Sampling
– Techniques for which you can specify the
probability that a participant will be selected
from a population.

Non-probability Sampling
– It is impossible to specify the probability of
selecting any one individual.
– The sample may or may not be representative
of the population.
Probability sampling
 Random sampling – a sample is drawn
such that each member of the population has an
equal probability of being included in the
sample.
– vs. random assignment – requires that
participants have been independently
assigned to groups.
Probability sampling

Systematic sampling – the population size is
divided by your sample size to provide you with
a number, k, for example; then from a random
starting point you select every kth individual.

Stratified sampling – the population is divided
into strata based on some population
characteristic and participants are randomly
selected from each stratum (therefore each
stratum is proportionally represented in the
sample).
Probability sampling

Cluster sampling – can be used when a
population list is not available and researchers
simply identify a number of clusters or groups
and include all participants in the cluster/group
in the sample.

Multistage sampling – a cluster technique
where smaller clusters are randomly selected
from larger clusters that were randomly selected
previously.
Non-probability sampling

Convenience sampling – using whatever
participants are easily available.

Quota sampling – convenience sampling in
which the goal is to select participants with
particular characteristics until you have enough.

Referral sampling – involves including
participants in the sample who have been
referred by other participants.
Sample and effect size

Sample size depends on:
– the power of the statistic
– your research design (how many conditions
you have)
– size of the effect
– variability of the data
Power revisited

You can increase power by increasing the
number of participants in your sample.

When deciding which sampling method to
use consider:
– How much time do I have?
– How much money do I have?
– How much help can I get?
Describing Your Participants

Participants
– How many?
– How Selected?
– Where do they come from?
– What age?
 max & min, mean and s.d
– Composition
 Gender breakdown
 Ethnicity
 Other important characteristic related to hypotheses
– Inclusions/Exclusion
– Compensation