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Chapter 9

PSYB01 Chapter 9

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University of Toronto Scarborough
Anna Nagy

PSYB01 - Chapter 9 Conducting Experiments 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 Straightforward Manipulation  Manipulate variable with relative simplicity by presenting written, verbal material to participants .  Straightforward manipulation:  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 . Staged Manipulation  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 dependent.  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: 1) Self-report 2) Behavioral 3) Physiological Self-Report Measures  Used to measure attitudes, judgment about someone’s personality characteristic etc.  Rating scales with descriptive anchors are most commonly used . Behavioral Measures  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  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 .  Variable can
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