STA429/1007 Assignment 10

Quiz on Tuesday Dec. 7th

Please revisit the infamous bunny data. Do a two-way multivariate analysis of variance, with time and drug as the independent variables, and force and stiffness as the dependent variables. The tests of interest are those for the main effect of time, the main effect of drug, and the drug by time interaction. Of these, the main effect for drug is by far the most important.

Following up any significant multivariate tests with the corresponding univariate tests using a Bonferroni correction, what do you conclude? Remember, the primary purpose of the study is to find out whether the drug increases bonding of the false tooth to bone. There are four multivariate tests for each effect. Let's agree to pay attention to Wilks' lambda.

Please bring your log and list files to the quiz. Write your conclusions on the reverse of the last page.

Just for reference, here are the details of the study again. But you probably just need to slightly edit your program from Assignment 5 (unless you messed it up, and then you may need to do a bit more editing). Note that this assignment is asking for a lot less detail than Assignment 5 did, so you can just cut out a lot of material.

An experiment in dentistry seeks to test the effectiveness of a drug (HEBP) that is supposed to help dental implants become more firmly attached to the jaw bone. This is an initial test on animals. False teeth were implanted into the leg bones of rabbits, and the rabbits were randomly assigned to receive either the drug or a saline solution (placebo). Technicians administering the drug were blind to experimental condition.

Rabbits were also randomly assigned to be "sacrificed" after either 3, 6, 9 or 12 days. At that time, the implants were pulled out of the bone by a machine that measures force in newtons and stiffness in newtons/mm. For both of these measurements, higher values indicate more healing. A measure of "pre-load stiffness" in newtons/mm is also available for each animal. This may be another indicator of how firmly the false tooth was implanted into the bone, but it might even be a covariate. Nobody can seem to remember what "preload" means, so we'll ignore this variable for now.

The variables are

  1. Identification code
  2. Time (3,6,9,12 days of healing)
  3. Drug (1=HEBP, 0=saline solution)
  4. Stiffness in newtons/mm
  5. Force in newtons
  6. Preload stiffness in newtons/mm