Suppose a horticulturist measures the aboveground height growth rate of four different ornamental shrub species grown in a greenhouse. The shrubs were grown from a random sample of seeds, and they were all grown in the same soil mixture and in the same size pot. To ensure that any slight differences in the environmental conditions throughout the greenhouse are not Macmillan Learning confounded with species, she randomizes the location of the pots throughout the greenhouse. The table contains a summary of her data. Population Sample Sample Sample Population description size mean standard deviation Species 1 _ m = 20 X1 = $3.887 cm/year $1 = 2.182 cm/year N Species 2 n2 = 20 X2 = 15.186 cm/year $2 = 3.915 cm/year W Species 3 n3 = 20 X3 = 16.824 cm/year $3 = 4.199 cm/year 4 Species 4 n4 = 20 X4 = 14.047 cm/year $4 = 2.952 cm/year The growth rate distributions of each sample are approximately normal, and the data do not contain outliers. The horticulturist uses a one-way analysis of variance (ANOVA) at a significance level of a = 0.01 to test if the mean growth rates of all four species are equal. Her results are shown in the table. Source SS df MS of variation f P-value f-critical Between groups 110.116 3 36.705 3.162 0.029 4.050 Within groups 882.223 76 11.608 Total 992.338 79 Show All