Question

Does the diet of a caterpillar (to be treated as a factor) affect the size of its head (dependent variable) once the caterpillar’s body weight (a covariate) is accounted for? To study the effect of forage quality on caterpillar head size, an ecologist raised caterpillars on three different diets: diet 1 was an artificial soft diet, diet 2 was a soft grass diet and diet 3 was a hard grass diet. The results are given overleaf.

a. Diet 1

Log body weight (mg)	1.1	1.3	1.4	1.4	1.5	1.6	1.7	1.8
Log head width (mm)	0.52	0.59	0.62	0.64	0.64	0.67	0.70	0.72

b. Diet 2

Log body weight	1.2	1.3	1.3	1.3	1.4	1.6	1.8	1.8
Log head width	0.47	0.50	0.48	0.47	0.52	0.59	0.60	0.61

3. Diet 3

Log body weight	1.1	1.4	1.4	1.5	1.6	1.6	1.7	1.7
Log head width	0.34	0.38	0.40	0.44	0.47	0.50	0.48	0.49

Collate and plot these sample data in a suitable way using R studio, then analyze the data by fitting an appropriate General Linear Model and testing associated null hypotheses. What conclusions do you draw?

Answer 1