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Lecture 5

# Lecture 5 - Jan 23.doc

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McGill University

Psychology

PSYC 305

Heungsun Hwang

Winter

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PSYC305 Lecture 5 - Jan. 23
Terminology Used in an Experiment:
• Independent variable (IV)
• Called a factor
• One-factor/Two-factor experiments
• Levels = the different values or categories of the independent variable/factor
• Single-factor Experiments
• Involve a single IV with two or more levels
• One-way independent-groups design
• One-way design with repeated measurements
• Factorial Experiments
• Involve more than one independent variable with two or more levels
• Two-way independent-groups designs
• When an experiment has two factors with two levels each, it is called a 2 x 2 experiment
One-Way ANOVA:
• Purpose:
• To test whether the means of k (≧ 2) populations significantly differ
• H 0 µ1 = µ2 … = µk
H : Not all µ’s are the same (at least one of the means is different)
• 1
• Example: One-Way ANOVA
• The statistics classroom is divided into three rows: front, middle, and back
• The instructor noticed that the further the students were from him, the more likely they were to
miss class or use an instant messenger during class
• He wanted to see if the students further away did worse on the exams
• DV = Exam score
• Factor (IV) = Class row
• Three levels: front, middle, and back
• H 0 µ1 = µ2 = µ3
• H 1 Not all µ’s are the same
• Prior Requirements/Assumptions:
The population distribution of the dependent variable is normal within each group
•
• The variances of the population distributions are equal (homogeneity of variance)
• Independent of observations
One-Way ANOVA: Basic Concepts • ANOVA = ANalysis Of VAriance
• Divides the variance observed in data into different parts resulting from different sources;
• Assesses the relative magnitude of the different parts of variance; and
• Exa

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