Biological Data Analysis: Homework 4

Due Tuesday, April 17

You must type this and all other homework assignments. Do not e-mail the assignment to me; turn it in early (at 322 Wolf) for a foreseeable absence, or turn it in late after an unexpected absence from class.

1. You're going to use the balance data set again. Analyze the nominal variable ("most disliked class") and the same measurement variable that you analyzed in homework 3. Get the histogram spreadsheet (linked from the textbook page on normality) and enter the values of the measurement variable for whichever class was disliked by the most people. Print the histogram.

2. Plot two more histograms; one for the data from question 1 after it has been log transformed, and one with a square-root transformation. Say whether you think the untransformed data looks close enough to normal, and if not, say which transformation you think is best.

3. Print a table showing the standard deviation of your chosen measurement variable and sample size for each disliked class. For each disliked class, you should give the standard deviation of the untransformed data; the standard deviation of the log-transformed data; and the standard deviation of the square-root transformed data. Based on comparing the standard deviations and sample sizes, say whether you think the data are homoscedastic enough to use Fisher's one-way anova.

4. Analyze the untransformed data using Fisher's one-way anova. Report the F-statistic, the degrees of freedom, and the P-value. Also do the Tukey-Kramer test and report the results in either a graph or table. Write a couple of sentences interpreting your results.

5. Even if you thought the untransformed data were normal and homoscedastic enough, pick the best transformation and analyze the transformed data using Fisher's one-way anova and Tukey-Kramer. Report the results as you did in question 4.

Return to the Biological Data Analysis syllabus