Basic Analysis and Graphing - SAS

142 Performing Oneway Analysis Chapter 5
Means/Anova and Means/Anova/Pooled t
Table 5.7 Description of the Analysis of Variance Report (Continued)
Mean Square
F Ratio
Prob>F
Is a sum of squares divided by its associated degrees of freedom:
• The Model mean square estimates the variance of the error,
but only under the hypothesis that the group means are
equal.
• The Error mean square estimates the variance of the error
term independently of the model mean square and is
unconditioned by any model hypothesis.
Model mean square divided by the error mean square. If the
hypothesis that the group means are equal (there is no real
difference between them) is true, then both the mean square for
error and the mean square for model estimate the error variance.
Their ratio has an F distribution. If the analysis of variance
model results in a significant reduction of variation from the
total, the F ratio is higher than expected.
Probability of obtaining (by chance alone) an F value greater
than the one calculated if, in reality, there is no difference in the
population group means. Observed significance probabilities of
0.05 or less are often considered evidence that there are
differences in the group means.
The Means for Oneway Anova Report
The Means for Oneway Anova report summarizes response information for each level of the nominal or
ordinal factor.
The Means for Oneway Anova report shows the following information:
Table 5.8 Description of the Means for Oneway Anova Report
Level
Number
Mean
Std Error
Lower 95% and Upper 95%
Lists the levels of the X variable.
Lists the number of observations in each group.
Lists the mean of each group.
Lists the estimates of the standard deviations for the group
means. This standard error is estimated assuming that the
variance of the response is the same in each level. It is the root
mean square error found in the Summary of Fit report divided
by the square root of the number of values used to compute the
group mean.
Lists the lower and upper 95% confidence interval for the group
means.