Download Analyzing Residuals of Carbohydrate Concentrations in Tropical Forests and more Lab Reports Statistics in PDF only on Docsity! Stat 401B Lab 2 Due September 15, 2008 Last week's lab looked at the data on nonstructural carbohydrates (NSC) concentrations (mg/g) in sapling stems in moist semi-evergreen and dry deciduous tropical forests in Bolivia. The data are available on the course Web site: http://www.public.iastate.edu/_wrstephe/stat401.html Use JMP to analyze the residuals for the two problems below. It is not sufficient to simply hand in JMP output. You must answer the questions completely. Turn in the JMP output attached at the end of your written (word processed) solutions. 1. One-sample problem. a. Use JMP to create residuals by subtracting off the sample mean from each of the 69 NSC concentrations. Use Analyze + Distribution to create JMP output that looks at the distribution of the 69 residuals. b. Refer to the histogram of residuals and indicate what you see and what this tells you about the condition that the population of NSC concentrations is normally distributed. c. Refer to the box plot of residuals. Are there any possible outliers? If so, what are the corresponding NSC concentrations, species and type of forest? What does the box plot tell you about the condition of identically distributed random errors? d. Refer to the Normal Quantile Plot of residuals and indicate what you see and what this tells you about the condition that the random errors come from a normal distribution. e. Summarize what you have learned about the conditions necessary for the statistical analysis of the NSC concentrations from your analysis of the residuals. 2. Two-sample problem. a. Use JMP to create the residuals for the two types of forest, dry and moist. Use Analyze + Distribution to create JMP output that looks at the distribution of the resulting 69 residuals. b. Refer to the histogram of residuals and indicate what you see and what this tells you about the condition that the random errors are normally distributed. c. Refer to the box plot of residuals. Are there any possible outliers? If so, what are the corresponding NSC concentrations, species and type of forest? What does the box plot tell you about the random errors being identically distributed? d. Refer to the Normal Quantile Plot of residuals and indicate what you see and what this tells you about the condition that the random errors are normally distributed? e. Comment on whether or not the data are consistent with the condition that both populations (dry and moist) have the same standard deviation. f. Summarize what you have learned about the conditions necessary for statistical analysis of data from your analysis of residuals. 3. Comment on the effect, if any, that your findings in problems 1 and 2 might have on inferences made using these data.
