HW1.Solutions - Biological Statistics II Biometry 3020 /...

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Unformatted text preview: Biological Statistics II Biometry 3020 / Natural Resources 4130 / Stat Sci 3200 Homework 1 Due on Thursday February 4 The questions below are from Kutner, Nachtsheim, Neter and Li Applied Linear Statistical Models, but some of these questions could be looked at using Splus/R in a manner similar to what was done with the Sparrow data in class. Data for certain problems (like the GPA data used in 1.19) may be found at the website: http://apps.csom.umn.edu/Nachtsheim/5th The inside cover of the back of the book also provides directions for getting data and other information including a student solutions manual. (Sorry not all the solutions are provided, but many are.) The following Splus/R commands might prove useful: names(CH01PR19)=c("GPA","ACT") plot(CH01PR19$ACT,CH01PR19$GPA) GPA.lm = lm(GPA~ACT,data=CH01PR19) summary(GPA.lm) anova(GPA.lm) new.ACT = data.frame(ACT=28) predict(GPA.lm,newdata=new.ACT,se.fit=T) 1. (KNNL 1.5, 1 point) When asked to state the simple linear regression model, a student wrote it as follows: . } { 1 i i i X Y E + + = Do you agree with this answer? No, the answer should be either . 1 i i i X Y + + = or i i X Y E 1 } { + = as the expected value of is . } { = i E 2. (KNNL 1.12, 2 points) In a study of the relationship for senior citizens between physical activity and frequency of colds, participants were asked to monitor their weekly time spent in exercise over a five-year period and the frequency of colds. The study demonstrated that a negative statistical relationship between time spent in exercise and frequency of colds. The investigator concluded that increasing the time spent in exercise is an effective strategy for reducing the frequency of colds for senior citizens. a. Were the data obtained in the study observational or experimental? The data are from an observational study . b. Identify two or three other explanatory variables that might affect both the time spent in exercise and the frequency of colds for senior citizens simultaneously. These might include other healthy habits such as taking a daily vitamin or having regular health check-ups. Grade Point Average Data 3. (KNNL 1.19, 4 points) The director of admissions of a small college selected 120 students at random from the new freshman class in a study to determine whether a students grade point average (GPA) at the end of the freshman year (Y) can be predicted from the ACT test score (X). The results of the study can be found in the file CH01PR19.txt. Assume that a first order regression model is appropriate.first order regression model is appropriate....
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HW1.Solutions - Biological Statistics II Biometry 3020 /...

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