It is common practice in many countries to destroy (shred) refrigerators at the end of their useful lives. In this process, material from insulating foam may be released into the atmosphere. The article “Release of Fluorocarbons from Insulation Foam in Home Appliances During Shredding” (J. of the Air and Waste Mgmt. Assoc., 2007: 1452–1460) gave the following data on foam density (g/L) for each of two refrigerators produced by four different manufacturers:
Does it appear that true average foam density is not the same for all these manufacturers? State and test the relevant hypotheses using a significance level of .05. Summarize your analysis in an ANOVA table.