Question

Mixed-Model ANOVA Article

            The first ANOVA was a mixed-model ANOVA to compare the scores of students from each disability group (no disability, reading disability, reading and math disabilities) using test (accomodation condition) as the within-subjects variable and disability as the between-subjects variable. Significant differences were found for the main effects of test, F(4, 184) = 6.55, p < .001, and disability group, F (2, 46) = 23.27, p < .001, and for the interaction between the two variables, F (8, 184) = 2.54, p < .05. Table 5 shows mean scores and standard deviations for each disability group.

            A series of one-way ANOVAs was run to follow-up the significant interaction between test condition and disability status. Four of the tests showed significant differences between the groups. Table 5 shows F-values for each test. Tukey HSD tests revealed that on each test that showed a significant difference, students without learning disabilities (LD) scored significantly higher than both students with RD and students with RMD, p < .01. Differences between students with RD and students with RMD were not significant on any test.

Table 5

Descriptive Statistics for Scores by Disability and Test Condition
	Disability
	NLD			RD			RMD			Marginal Means
Test	M	SD		M	SD		M	SD				F
Standard	30.88	13.23		14.14	9.75		9.70	6.21		18.33		23.16*
Computer-read text	33.28	13.22		14.92	11.32		9.77	8.65		19.34		19.02*
Video	34.28	16.44		11.89	8.64		10.33	8.78		19.72		20.73*
Constructed response	23.63	13.62		20.33	8.90		18.23	6.85		13.79		2.08
Two accommodations	20.56	11.22		16.87	7.64		17.81	5.47		18.02		1.34
Comprehensive	25.13	14.19		11.64	7.61		9.40	8.04		15.36		10.81*
Marginal means	29.44			12.78			8.49
NLD = nonLD.      RD = reading disability.       RMD = reading and math disabilities.
aFollow-up one-way ANOVAs, df = 2, 46.
*p < .01.

2. In the mixed-model ANOVA, should the null hypothesis that students in the different disability groups will score similarly on the tests be accepted or rejected?

3. How many group means are involved in the comparison of the disability groups?

4. How many measures of the within-subjects variable are there?

5. How many subgroup means are involved in the comparison for the significant interaction?

Answer 1