Chapter Nine: Conducting Experiments
Selecting Research Participants
The method used to select participants has implications for generalizing the research results.
Probability testing is crucial for scientific polls because it can accurately describe the population whereas convenience sampling affects one’s
ability to generalize the results to a larger population from the samples.
You need to determine a sample size. Increasing the sample size increases the statistical significance because larger samples give more accurate
estimates of the population.
Manipulating the Independent Variable
To manipulate an independent variable one must construct an operational definition of the variable (turn a conceptual variable into a set of
The independent and dependent variables must be introduced within the context of the total experimental setting which is called setting the
In setting the stage you have to (1) provide participants with the informed consent information needed for your study and (2) explain why the
experiment is being conducted.
No clear cut rules for setting the stage or translating conceptual variables into specific operations.
Types of Manipulations
Straightforward Manipulations and Staged Manipulations
Manipulations in which the variable in simply manipulated by presenting written, verbal or visual material to participants.
Most memory research relies on straightforward manipulations.
Most manipulations of independent variables in all areas of research are straightforward.
Not as straightforward. Stage events that occur during the experiment in order to manipulate the independent variable successfully.
Used because (1) the researcher may be trying to create some psychological state in the participants or (2) it may be necessary to stimulate
some situation that occurs in the real world.
Staged manipulations frequently employ a confederate (accomplice).
Easier to interpret results when the manipulation is straightforward.
Strength of the Manipulation
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.
Strong manipulation is important in early stages of research.
Two considerations when using the strongest manipulation: (1) may involve a situation that rarely occurs in the real world and (2) ethics.
Cost of the Manipulation
Straightforward manipulations are less costly than complex staged ones.
Measuring the Dependent Variable
Self report, behavioural, and physiological.
Self Report Measures
Can be used to measure attitudes, personality, confidence etc.
Ratings with descriptive anchors are most commonly used.
Direct observations of behaviours.
Recordings of responses of the body.
Galvanic skin response (GSR)- a general measure of emotional arousal and anxiety that measures the electrical conductance of the skin.
Electromyogram (EMG)- measures muscle tension and is frequently used as a measure of tension or stress.
Electroencephalogram (EEG)- a measure of electrical activity of brain cells. Can be used to record general brain arousal.
Also temperature, heart rate, blood and urine analysis.
Magnetic resonance imaging (MRI)- provides an image of the brain structure.
Functional MRI (fMRI)- scan areas of the brain to see which parts of the brain is active.
Sensitivity of the Dependent Variable
The issue of sensitivity is important when measuring human performance.
Ceiling effect- the independent variable appears to have no affect on the dependent measure only because participants quickly the maximum
performance level. Vice versa is the floor effect.
Cost of Measures