For this post, I will answering the following questions.
Question 1:
A researcher is interested in the effects of drug against stress reaction. She gives a reaction time test to three different groups of subjects: one group that is under a great deal of stress, one group under a moderate amount of stress, and a third group that is under almost no stress. The subjects of the study were instructed to take the drug test during their next stress episode and to report their stress on a scale of 1 to 10 (10 being most pain).
Report on the drug and stress level by using R. Provide a full summary report on the result of ANOVA testing and what does it mean? More specifically, report using the following R functions:
After running a summary report after using ANOVA, we first see that the degrees of freedom results in 2 meaning that there are two degrees of freedom associated with the variability in stress levels because of the stress group. As for Sum Sq or Sum of Squares, the value 82.11 represents the sum of squares associated with the stressGroup variable. Given the larger value, it can be interpreted that there is a significant amount of variability in stressLevel that is being explained by the stressGroup. Moving on to Mean Sq, 41.06 is the value associated with the stressGroup variable. Seeing how the value is larger than the residuals value, it can be taken away that the stress group indeed explains more variability in stressLevel than expected by random chance. For the F value, the summary produced the value of 21.36 which seems to indicate that it is a large value coupled with a rather small p-value (4.08e-05). Thus, the stress group variable has a statistically significant effect on stress levels.
Question 2:
From our Textbook: Introductory Statistics with R, Chapter 6, Exercises 6.1, pp. 127
The zelazo data (taken from textbook's R package IWsR) are in the form of a list of vectors, one for each of the four groups. Convert the data to a form suitable for the user of lm and calculate the relevant test. Consider t tests comparing selected subgroups or obtained by combining groups.
2.1 Consider ANOVA test (one-way or two-way) to this dataset (zelazo)
Recommendations
After reflecting upon the zelazo dataset, it can be seen that the one-way ANOVA test is more appropriate given that data set contains only one independent variable (type of training) with four levels like “active”, “passive”, “none”, and “ctr.w8” which means control. Seeing that one-way ANOVA tests work best when given a categorical independent variable (factor) with more than two levels (groups), it is clear that this test is more fitting to the problem than two-way ANOVA. We have four groups and one factor.
~ Katie
