Final Exam, Biostatistics, Fall 2006

ID Number:______

Format. Turn in a paper copy of your typed exam paper (no handwritten papers will be accepted, but small handwritten notes on graphs, printouts etc…. are OK) by 10am Monday, 11 December 2006. Email submissions will not be accepted. I will be in my office, 3086-C Bowman Oddy from 8-10am on Monday, 11 December 2006 to receive your exams. For people who work at the LEC, you can also deliver your exam to Dr. Jon Bossenbroek between 8-10am, Monday, 11 December 2006. You can give me your exam at any time before this, but it must be personally handed to me.

Scenario: A group of researchers want to know how production of bottom dwelling algae responds to the presence/absence of zebra mussels and other grazers (small invertebrates). They used a factorial experimental design to test this. The best available measurement of production (NPP) is taken by measuring O2 evolution, but this method is very labor intensive. They also take measurements of electron transport rates (ETR) with a flourometer, a device that is very easy to use (point and click). ETR should provide a good index of photosynthesis and hence overall production. However, the florometer method is not widely accepted and they must demonstrate that this method corresponds to NPP.

Their experimental design consisted of placing aglae covered rocks into a total of 64 large tanks. Some of the containers received zebra mussels (N=32), whereas some did not (N=32). Some (N=32) received other grazers while the others did not (N=32). The tanks were all contained in a single climate controlled room and the assignment of treatment to a particular tank was completely random. The treatments were factorial, so that there were 16 replicates of each treatment combination (cell). ETR and NPP measurements were taken from a single rock within each tank. They considered tanks to be experimental units because zebra mussels and other grazers were applied independently to each tank.

Instructions: For each question 1) Decide what test they should do 2) List the null and alternative hypotheses being tested 3) Explain as completely as you can why the test you chose was better than other possible alternatives 4) Carry out the test using SAS, another program, or by hand, provide calculated and critical values of you statistic (t, F, etc………) and all other relevant information needed for a reviewer to judge the statistics. 5) Provide graphs that compliment your analysis 6) Explain how they should interpret their results. Neatness and organization are important because they help me to easily evaluate your answers.

The researchers would love to use Bayesian statistics, but they don’t know how, so they must use the old standby frequentist approaches that they learned in stats class.

Their specific questions are:

1) How well do NPP and ETR correspond? (12 pts) 2) Does production change with presence of zebra mussels or other grazers? You can answer this question using either NPP or ETR, but you must justify why you chose one or the other. (14 pts)

3) Critique their experimental design. What was good, what was bad? How could it be improved? Give details about sample size, arrangement, sampling etc……. (10 pts)

4) Describe an “in lake” study that they could do to answer the same questions. Give specifics about sample size, treatments, arrangement, sampling etc…….(10 pts)

5) What are the advantages and disadvantages of doing the “in lake” study compared to the above laboratory study? (4pts)