Minitab presents 95% confidence intervals for each level of the factor. When the p-value in the analysis of variance table indicates that there is a difference among the factor level means, use the interval plot of level means and individual confidence intervals to explore the differences:

·    Each dot represents a sample mean.

·    Each interval is a 95% confidence interval for the mean of a population. You can be 95% confident that the population mean for each level is within the corresponding interval.

·    If the intervals for two means do not overlap, it suggests that the population means are different. You should interpret these intervals with caution, however, because your rate of type I error increases when making multiple comparisons. Thus, when making multiple comparisons, you should use one of the five available methods for controlling the rate of type I error.

In the paint hardness results, the intervals for the means of Blend 2 and Blend 4 do not overlap. This suggests that the population means for these levels are different.