Sources of Variation Section 1.1 1.1.1  B. 1.1.2  B & C. 1.1.3  A. 1.1.4  C. 1.1.5  E. 1.1.6  B. 60.34 if rigid librarian predicted number of uses for items = {92.19 if eccentric poet 1.1.7  1.1.8 a. The inclusion criteria are having a clinical diagnosis of mild to moderate depression without any treatment four weeks prior and during the study. b. The purpose of randomly assigning subjects to the groups is to make groups very similar except for the one variable (swimming with dolphins or not) that the researchers impose. Volunteering for a group could introduce a confounding variable. c. It was important that the subjects in the control group swim every day without dolphins so that this control group does everything (including swimming) that the experimental group does except that when they swim they don’t do it in the presence of dolphins. Without this we wouldn’t know whether just swimming causes the difference in the reduction of depression symptoms. d. Yes, this is an experiment because the subjects were randomly assigned to the two groups. 1.1.9. Observed variation in: Sources of explained variation Sources of unexplained d. substantial reduction variation in depression symptoms Inclusion criteria a. swimming with dolphins or not • g. problems in the personal lives of the subjects during the study • b. mild to moderate depression • c. no use of antidepressant drugs or psychotherapy four weeks prior to the study • h. illness of subjects during the study Design • e. swimming • f. staying on an island for two weeks during the study 1.1.10  Color of a sign is the explanatory variable with white, yellow, and red being the levels. 1.1.11  Observed Variation in: Sources of explained variation Sources of unexplained f. whether the student variation obeyed the sign Inclusion criteria a. color of the sign b. whether the subject was left-handed or right-handed • c. time of day • e. age of subject d. attitude of student e. age of subject 1.1.12 a. The value 6.21 represents the overall mean quiz score, 5.50 represents the group mean quiz score for people who used computer notes, and 6.92 represents the group mean score for people who used paper notes. b. We look to see how far 6.92 and 5.50 are from one another or from the overall mean of 6.21 to determine whether the note-taking method might affect the score. The number 1.76 represents the typical deviation of an observation from the expected value, in this case, from the overall mean. The number 1.61 represents the typical deviation of an observation after creating a model that takes into account whether the person is using computer or paper notes. d. Because the standard deviation of the residuals represents the leftover variation, we can see that after including the type of notes as an explanatory variable in our model the unexplained variation has been reduced (down to 1.61 from 1.76). This tells us that knowing the type of note-taking method enables us to better predict scores. c. 1.1.13  Random assignment should make the two groups very similar with regard to variables like intelligence, previous knowledge, or any other variable and thus likely eliminate possible confounding variables. 1.1.14 a. This table shows us possible confounding variables but then shows that subjects in the two groups are quite similar with regard to these characteristics, thus ruling out these possible confounding variables. b. We would want the p-values to be large, so we could say that we have little to no evidence that there is a difference in mean age, proportion of males, etc. between the two groups. We want our groups to be very similar going into the study, so a causal conclusion is possible if we find a small p-value after applying the treatment(s).