18.2 A botanist measured the 3-day growth, in inches, of his marijuana plants at two different times (variables: “pregrowth” and “postgrowth”)

under four different growing conditions (variable: “peatsoil”). He felt that the initial growth rate influenced the second rate of growth. The scientist’s main concern was the effect of soil type on growth rate during the second growth period. The problem was that he somehow wanted to statistically account for any differences in the second growth period that might be related to the first rate of growth. His ultimate quest was to identify any significant differences in the four samples that were grown in soils containing different percentages of peat. Select the correct statistical method, write the null and alternative hypotheses, do the analysis, interpret the results, and answer the botanist’s questions.