PSYB01 - Chapter 9
Selecting Research Participants
Sample may drawn from population using probability sampling / non-probability sampling .
Use probability when it’s important to accurately describe the population.
Use non-probability sampling when research is testing hypotheses .
Focus of study is relationship between variable/test prediction derived from theory .
Can use non-probability haphazard / “convenience” sampling .
Larger sample size = result will statistically significant = more accurate estimate of population .
Manipulating The Independent Variable
Need to construct operational definition of variable to manipulate the independent variable .
Need to turn conceptual variable into set of operation (e.g. instructions/events/stimuli) .
”Setting the stage”: Independent and dependent variable must introduced within context of setting .
Two things to do in setting the stage:
1) Provide the participant with informed consent information .
2) Explain to participants why experiment is being conducted .
No clear-cut rules, but setting must seem plausible to participants .
Types of Manipulations
Manipulate variable with relative simplicity by presenting written, verbal material to participants .
Manipulate variable with instructions and stimulus presentation .
Vary difficulty of material to be learned/way of question asked .
Involve participants in ongoing social acting ability .
Individuals perceive not as experiment but as real experience .
Stage events occur during the experiment in order to manipulate the independent variable .
Refer as staged / event manipulation .
Demand great deal of ingenuity and even some acting ability .
Used to involve participants in ongoing social situation .
Most frequently used for 2 reasons:
1) Try to create some psychological state in participants (e.g. anger/frustration)
2) To stimulate some situation that occurs in real world
Confederate: Frequently employ in staged manipulation .
Confederate: Appear to be another participant in experiment, but actually part of manipulation.
Useful to create particular social situation .
Disadvantages: Complex manipulation is difficult to interpret .
Difficult to replicate the experiment for other researchers .
Strength of Manipulation
Research has to choose the levels of independent variable .
General principle is to make manipulation as strong as possible .
Strong manipulation will maximizes difference between 2 groups . Increase chances that independent variable will have statistically significant effect on
Principle of using strongest manipulation possible should tempered by 2 consideration:
1) Strongest possible manipulation may involve situation that rarely occurs in real world .
2) Ethics-manipulation should be strong as possible within bounds of ethics .
Cost of the Manipulation
Limited monetary resources may not be able to afford expensive equipment/salaries for confederation .
Use straightforward presentation of written/verbal material is less costly .
Measuring The Dependent Variable
Types Of Measures:
Dependent variables are one of 3 general types:
Used to measure attitudes, judgment about someone’s personality characteristic etc.
Rating scales with descriptive anchors are most commonly used .
Behavioral Measures: Direct observation of behaviours .
Sometime researcher may record whether or not given behavior occurs .
Need to decide whether to record the # of times a behavior occurs in given time period .
Rate of behavior: How quickly a response occurs after a stimulus .
Reaction Time: How long a behavior lasts, measure of duration .
Physiological measures: Recordings of responses of body .
Galvanic skin responses (GSR): Measure of general emotional arousal and anxiety .
Measure electrical conductance of skin, changes when sweating occurs .
Electromyogram (EMG): Measure muscle tension, used as measure of tension/stress .
Electroencephalogram (EEG): Measure of electrical activity of brain cells .
Used to record general brain arousal as response to different situation .
Magnetic resonance imaging (MRI): Provide image of brain structure of individuals .
Functional MRI (fMRI): allows researcher to scan areas of brain while research participants perform
physical/cognitive task .
Sensitivity of Dependent Variable
Sensitivity: Important when measuring human performance .
Ability of measure to detect difference between groups .
Ceiling effect: Independent variable appears to have no effects on dependent measure only .
Since participants quickly reach the maximum performance level .
e.g. When performing easy task that everyone does well .
Floor effect: When task is so difficult which hardly anyone can perform well .
Multiple Measures Often desirable to measure more than one dependent variable .