Research Methods in Biology
Homework 2
Due Tuesday, Sept. 11

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 want to know whether pesticides cause the sex ratio of wild mice to be different from the 1:1 ratio expected under the XX/XY sex determination system that mammals use. You go to a golf course that uses lots of pesticides and trap 23 mice with live traps baited with peanut butter. What is your biological null hypothesis? What is your statistical null hypothesis?
  2. There are 14 male mice and 9 female mice. Perform the appropriate statistical test; what do you conclude?
  3. If the true proportion of male mice really is 14 out of 23 (0.609), what sample size would give a significant deviation from the null hypothesis 90 percent of the time?
  4. Find the sample size needed to detect a significant deviation from the null hypothesis 90 percent of the time for at least 10 different values of the true proportion of males (somewhere between 51 and 100 percent males). Plot this on a computer-generated graph, following the format specified in the Guide to Good Graphs. Write a sentence or two about what you learned from this graph.
  5. Is your sample of mice a good random sample? If so, what makes it a good sample; if not, what's wrong with it, and how could you get a better sample?

    Here are four practice questions for the exam. For each experiment, list the variables that are mentioned in the description, and say whether each is an attribute, 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.

  6. 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.
  7. 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.
  8. 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 measure the height and diameter of each tree. You put a radio collar on a squirrel, then record the amount of time it spends in each tree. You do this for six squirrels.
  9. 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."

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This page was last revised September 6, 2007. Its URL is http://udel.edu/~mcdonald/stathw2.html