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PSYC 3020 (50)
Dan Yarmey (47)

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University of Guelph
PSYC 3020
Dan Yarmey

Maass, A (1996). Logic and methodology of experimental research in eyewitness psychology  Random assignment to experimental conditions guarantees that the experimental groups are equivalent within the limits of a specified error probability. There is always random variation within groups  experimental control and randomization enable the psych researcher to draw conclusions about causality Basics  Hypothesis o First step o Testability restricted by practical, logical, and ethical issues o Many problems of eyewitness psychology cannot be investigated experimentally  Ex) violence and life threat influence on eyewitness accuracy o However, you can test some things that cant be tested in reality  Operationalization of independent variables o Must have two different levels or degrees in which you’re measuring (long vs. short time delay) o Interaction: one independent variable influences another  ex) the race of an offender and the race of a victim interact and influence one another  Construct validity o Constructs are more complex concepts that are difficult to operationalize  Ex) the arousal of a witness, or instructional bias o Construct validity means the independent variable has to be operationalized in a way that represents the underlying construct as broadly as possible and is not confounded with any other constructs  Ex) if emotional arousal is to be studied, must make sure that subjects are indeed substantially aroused  Ex) if measuring effect of a weapon presence has on eyewitness memory, criminal in one group should hold object in hand that is similar in size to the gun that the criminal in the other group is holding. o It’s important that subjects perceive the experimental procedure according to the experimenter’s intentions (do a pilot study for this) o Conceptual replication: construct validity can also be established by investigating the same hypothesis in different experiments with different operationalizations Maass, A (1996). Logic and methodology of experimental research in eyewitness psychology  Internal validity o Make sure there are no confounding/extraneous variables that would explain changes in the dependent variable (should only be attributed to a change in the independent variable under measure)  Measurement of the Dependent variables o Person description and Person identification  Dependent variable can rarely be reliably assessed in eyewitness identification research because the correctness of the description or the identification can rarely be controlled, as opposed to in the field  Researcher can objectively control the correctness of an identification in an experimental setting, as he or she knows the true identity of the criminal o Incorrect identifications and the tendency to guess  Incorrect identification: a witness identifies an innocent suspect  False rejection: the actual criminal is present in the line-up, but they are not identified  Signal detection theory: accuracy is partly determined by memory strength, and partly by decision criterion, which determines the minimum amount of perceived similarity betwe
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