A sample of 24 older homes are randomly divided into four groups and retrofitted with different types of insulation. The response variable is the relative decrease in energy usage. The data is summarized in Table 6.23. Construct the ANOVA table, and draw the appropriate conclusion assuming α = 5%. 

Table 6.23 Summary for Exercise 4. Insulation Type 1 2 3 4 N 6 6 6 Mean 15.5 22.3 24.6 31.8 Std. Deviation 4.2 5.3 5.0 4.9