Biological Data Analysis: Homework 1

Due Tuesday, Sept. 2

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. Choose an article from the lab you're in (if you're in a lab) or from your favorite scientific journal. It should be a regular-sized article (not a brief note) in a specialized journal (not Science, Nature, or PNAS). If you don't have a lab or a favorite journal, I recommend Evolution. Make sure the article has some kind of statistical test in it. Read through it and identify at least six variables that are analyzed in the paper. For each variable, provide the name of the variable (such as "LAM"), and if it's not obvious from the name, give a short explanation of what the variable is (such as "length of the anterior adductor muscle scar on a mussel shell"). Then say whether the variable is a measurement variable, a nominal variable, or a ranked variable. If a measurement variable has been converted to a nominal variable, or if the percentages from a nominal variable have been analyzed as if they were a measurement variable, mention this. You must have at least six variables; if you don't have six, do more than one paper.

2. Next, find one statistical test that is used in the paper. It may be difficult at this point in the class, but try to anwer the following:

3. Give the citation information (authors, year, article title, journal, volume, page numbers) for the article or articles you've used.

Mmmmm, bonus: Everyone who finds an article with a true ranked variable (not a measurement variable converted to a ranked variable for a non-parametric test) gets a donut at the next class.

Here are four practice questions for the final exam. For each experiment, list the variables that are mentioned in the description, and say whether each is a nominal, measurement, or ranked variable. Don't list variables that are not mentioned in the description; for example, don't list "weight of mice" for the first experiment.

4. You want to know whether food coloring affects the activity of mice. You feed 12 mice Purina Mouse Chow and 15 other mice Purina Mouse Chow with 10 mg yellow food coloring/kg added. You record how many hours a day each mouse spends running on its exercise wheel. You do this on each of 21 days.

food with or without food coloring: nominal
hours a day running on the wheel: measurement
number of days since the start of the experiment: measurement
name of each mouse: nominal (this one is pretty subtle, and we haven't covered why this should be considered a variable yet, so don't worry if you didn't get this

5. You want to know what kind of cat people like the best. You go to an animal shelter and take a picture of each cat, which you clip to its cage. When a cat gets adopted, the staff of the shelter pins the photo to a bulletin board, starting at the upper left and working their way down. Once all the cats are adopted, you record the position of each photo and the pattern of the cat: solid orange, orange and white, solid black, black and white, calico, etc.

pattern of the cats: nominal
order in which the cats were adopted: ranked

6. You're trying to figure out what trees squirrels like the best. You go to White Clay Creek State Park and find an area with a mix of oak, maple, sycamore, redbud, and dogwood trees. You randomly pick 20 of each species of tree, measure the height and diameter of each tree, and count the number of squirrel nests in each tree.

type of tree (oak, maple, etc.): nominal
height: measurement
diameter: measurement
number of squirrel nests per tree: measurement (unless there were just zero or one nest per tree, then it would be nominal

7. You want to know what percentage of college students in different majors accept the evidence for evolution. You survey 1,372 undergraduates and ask each student their major, what year they are, their gender, their GPA, how many biology classes they've taken, and whether they agree or disagree with the statement, "All living organisms on earth, including humans, have evolved over billions of years from earlier life by natural processes."

major: nominal
year: measurement (I'm assuming you've found some students who have been here for five or six years)
gender: nominal
GPA: measurement
number of biology classes: measurement
agree or disagree: nominal

Return to the Biological Data Analysis syllabus

Return to John McDonald's home page

This page was last revised August 25, 2014. Its URL is