Question: Moore and McCabe (1993) describe a study involving three groups of children being taught reading by three different methods (labelled BASAL, DRTA and STRAT). The three groups of 22 were assigned randomly and pretests of their reading comprehension (COMP) showed no differences between the groups. Summary statistics for their COMP scores at the end of the study are shown below.

1. Construct an analysis of variance (ANOVA) table for these data (Note: the ‘total sum of squares’ is 2871). Carry out the F-test; state the hypothesis being tested and the critical value for a significance level of 0.05. Interpret the result of the test.
2. Explain what is meant by the term "Least significant difference’ (LSD). Apply the LSD method to the data and interpret the results. What reservations would you have in applying the LSD method in a situation where there is a large number of groups?
3. What assumptions underlie the test you have carried out? Explain how a ‘residual analysis’ could be carried out (given the raw data) to assess the validity of these assumptions.

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