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Chapter 6

Chapter 6 Notes 97-03.doc

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David Nussbaum

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PSYB01 Chapter 6 – True Experiments I - Merzenich and colleagues examined whether healthy participant aged 60 years or older would show improved mental abilities following brain plasticity training - Variables differ in the degree to which they can be controlled or manipulated - True Experiment: Researcher has complete control over manipulation of independent variable, standard approach to establish causality Basics of Experimentation - Researcher controls with whom, with what and how the study is conducted - Experimental Control: Holds constant as many extraneous variables as possible, if variable s are constant, they cannot account for results of experiment - Randomization: Procedures to counteract bias o Memorizing words (we remember first and last, primacy effect and recency effect), must move the words around so that the words aren’t gonna be in the same place o Random assignment: Each participant has an equal likelihood of being placed in either control or experimental groups (chance procedure) o Ex post facto: participants selected and grouped after the fact or on the basis of a particular characteristic - Independent Variables: something the researcher manipulates in some way in order to determine its effects on a dependent variable, often referred to as factors o Single-factor experiment: an experiment with only one independent variable o Multi-factorial designs: experiment with more than one independent variable o Condition/Treatment: a particular way in which participants are treated o Experimental group vs. comparison group vs. control group o Control group provides baseline against which the treatment can be compared - Dependent Variables: o Posttest: measurement of the outcome in both groups after the experimental group has received the treatment o Pretests: measure dependent variable prior to the experimental intervention o Using identical pre- and posttests is to be avoided because performance is likely to be influenced by practice of taking the same measure twice - Control Variables: Used to show that these factors do not explain results, if they do, the nthe results are considered to be confounded o Challenge in identifying or selecting which variables to be controlled for or held constant o Some variables are easy to keep constant: Time of day, temperature, instructions, etc. Research Design Alternatives PSYB01 Chapter 6 – True Experiments I - Between-Subjects Design: independent groups of participants receive different levels of independent variable o Same participants never receive all levels of independent variable : therefore, a large number of people are needed for study - Randomization and Matching o Ensure that there are as few differences as possible among participants in various treatment groups o Individual differences are equalized or neutralized when researchers use random assignment to form experimental and control groups o Must also have a pretest after randomization so that it is actually randomized o Randomized comparative change design/pretest-posttest control group design: Randomized experimental design with a pretest and posttest o Act of taking pretest may cause change o Randomization removes bias from assignment process but only by relying on chance which can result in some intergroup differences o Matching: pairing persons on the basis of similarity of gender, age, year in school or some other objective characteristic o Matched-pairs design: first match in pairs and then randomly assign one to experiment and one to control - Within-subjects Design: all research participants receive all levels of the independent variable o Repeated-measures, within-subjects design: when same participant is tested repeatedly over time, each participant serves as their own control o Fewer participants needed because they all receive the treatment o Longitudinal research design: collect data for decades, participants followed over lifespan and data are ordered in time so that they can be developmentally examined o Carryover effects: if performance in one condition affects performance in a subsequent condition o Randomization ensures that any differences in treatment orders are due to chance only - Counterbalancing: Technique to control for order of treatments that ensures that each treatment or level of the independent variable occurs in each time period of the experiment o As number of treatments/
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