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Week9_Notes_Pt2

# Week9_Notes_Pt2 - Psych 100A Week 9 Discussion Notes Part 2...

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Psych 100A Week 9 Discussion Notes Part 2: The One-Factor Between-Subjects Analysis of Variance November 27, 2009 Dawn Chen Remember that t -tests are used when we have only two groups of observations. When there are more groups, we usually use a family of tests called analysis of variance (ANOVA). The one-factor (or one-way) between-subjects ANOVA is a statistical hypothesis testing procedure that is used when we have one independent variable with three or more levels, each of which is either administered to (if the independent variable is a treatment) or possessed by (if the independent variable is a characteristic of the subject, such as ethnicity) a separate, independent group of subjects. For example, let’s consider the following experiment: A social psychologist was interested in the effect of crowds on response to emergency situations. To evaluate this effect, each of 12 subjects was randomly assigned to 1 of 3 conditions: alone, 2 other people in the room, or 4 other people in the room. Subjects saw smoke coming from the next room. The researcher measured how many minutes it took subjects to react and do something. The results are shown in the following table: Alone 2 other people 4 other people 8 8 10 8 6 8 9 15 24 11 19 18 Mean 9 12 15 Here, the independent variable is the number of other people in the room, with three levels: 0, 2, and 4. Since the independent variable has three levels, each of which is given to a separate, independent group of subjects, the one-factor between-subjects ANOVA is the appropriate test for this experiment. In this example and in general, we are still interested in whether the mean scores on the dependent variable among the different groups are significantly different. In this example, we

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Week9_Notes_Pt2 - Psych 100A Week 9 Discussion Notes Part 2...

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