An article in Industrial Quality Control (1956, pp. 5–8)

describes an experiment to investigate the effect of the type of glass and the type of phosphor on the brightness of a television tube. The response variable is the current necessary (in microamps) to obtain a specified brightness level. The data are as follows:

Phosphor Type Glass Type 1 2 3 280 300 290 1 290 310 285 285 295 290 230 260 220 2 235 240 225 240 235 230

(a) Is there any indication that either factor influences brightness? Use ???? = 0.05.

(b) Do the two factors interact? Use ???? = 0.05.

(c) Analyze the residuals from this experiment.