Yield (unspecified unit Wheat Yields for F 42 40 38 Fertiliser | Yield (unspecified units) 36 30 31 35 34 37 37 33 36 37 34 42 39 40 36 35 36 32 40 42 41 38 35 30 A B C D Fertiliser > describeBy (Yield, Fertiliser, mat = TRUE, skew=FALSE, range=FALSE, digits=3) item groupl vars n mean sd se X11 X12 X13 X14 PWNH A 1 5 33.40 2. 881 1.288 1 4 35.75 1.893 0.946 1 6 38.00 2.757 1.125 1 5 39.20 2.775 1.241 > summary (fert.model) Of Sum Sq Mean Sq F value Pr(>F) Fertiliser 3 99.45 33.15 4.704 0.0154 * Residuals 16 112.75 7.05 > leveneTest(fert.model) Levene's Test for Homogeneity of Variance (center = median) Of F value Pr(>F) group 3 0. 4331 0.7322 16