7. Oneway ANOVA
When to use a Oneway ANOVA
Oneway ANOVA is a generalization of the independent samples t-test. Recall that the independent samples t-test is used to compare the mean values of 2 different groups. A Oneway ANOVA does the same thing, but it has the advantage of allowing comparisons between more than 2 groups. In psychology, for example, we often want to contrast several conditions in an experiment; such as a control, a standard treatment, and a newer “experimental” treatment.
Because Oneway ANOVA is simply a generalization of the independent samples t-test, we use this procedure below to recalculate our previous 2 groups example. Later, we will do an example with more than 2 groups.
Example 7.1
Let’s return to our example of the pizza vs. beer diet. Our research question is: “Is there any weight gain difference between a 1-week exclusive diet of either pizza or beer?”
An Oneway-ANOVA is a generalization of the independent samples t-test in which we can specify more than 2 conditions. If we only specify 2 conditions, however, the results will be exactly the same as the t-test. The calculations are somewhat different, but the resulting “p-value” will be the same, and therefore the research conclusion will always be the same.
ANOVA operates on the principle of “partitioning the variance.” There is a total amount of variance in the set of data above. This total variance is found by subtracting each value (e.g., 1,2,2…) from the mean for all 10 people (
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