# CHAPTER 9.docx

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22 Apr 2012
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CHAPTER 9
SELECTING RESEARCH PARTICIPANTS
- Samples may be drawn from the population using probability sampling or nonprobability
sampling techniques
- Probability sampling used when it is important to accurately describe the population (i.e.
conducting scientific polls)
- Nonprobability haphazard or “convenience” sampling methods used when studying the
relationships between eh variables and testing prediction derived from theories of behaviour
- Sample size also important larger sample = results statistically sig.
MANIPULTAINT THE INDEPENDENT VARIABLE
- To manipulate independent variable you have to construct an operational definition of variable
must turn a conceptual variable into a set of operations; specific instruction, events, and
stimuli to be presented to the research participants
- Independent and dependent variables must be introduced within the context of the total
experimental setting aka. “setting the stage”
Setting the Stage
- Provide the participants with the informed consent information needed for study
- Explain to participants whey experiment is being conducted
- If deception is necessary, you must address eh deception during the debrief
Types of Manipulations
1) Straightforward Manipulations
Can manipulate by presenting written, verbal, or visual material to participant
Manipulations manipulate variables with instructions and stimulus presentation
Stimuli may be presented verbally, in written form, via videotape, or with a computer
2) Staged Manipulations
Used for two reasons: the researcher may be trying to create some psychological state
in the participants (anger, frustration, etc); OR; because it is necessary to simulate some
situation that occurs in the real world
Frequently employ a confederate appears to be another participant in an experiment
but is actually part of the manipulation
Confederates may be used in field experiments as well as laboratory research
Such procedures allow for a great deal of subtle interpersonal communication that is
hard to put into words making it difficult for other to replicate the experiment
A complex manipulation is difficult to interpret
Strength of Manipulation
- Simplest experimental design has two levels of independent variable
- A strong manipulation maximizes the differences between the two groups and increases the
chances that the independent variable will have a statistically significant effect on the
dependent variable
- The principle of using the strongest manipulation possible should be tempered by at least two
considerations; first, the strongest possible manipulation may involve a situation that rarely
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