Biostatistics Mini-project 4

Your solution should be written up as a report (an essay). You should write as though you were writing a methods and results section for a paper you would submit. Rephrase the question posed, write a brief summary of your results making clear what test you used (including degrees of freedom and other relevant parameters) and whether the test was one or two-sided, if appropriate. Graphics can be very useful and can make your point for you better than words do. Include them when appropriate. Your write-ups should be kept short. You should NOT do every test you know to do with these data and then discuss all possible outcomes. You SHOULD pick an appropriate test, conduct it, and report the results of it. NEVER, NEVER include raw Minitab (or other software) output. When appropriate, you can format your own table and include the relevant parts of the Minitab output. You should also comment on the experimental design and how it impacts your conclusions. If the data are observational, then there may be numerous factors impacting the significance of the test (or the lack of significance) and the results may not be due to the factor that is distinguishing the groups but by some uncontrolled factor. True experiments also differ in the quality of their design for controlling for miscellaneous factors. Mention any problems with the design you notice.

The grading rubric for this assigment can be found through the following link: Grading Rubric for the Projects

Problem: Compare the relationship between liver weight and body weight in three treatment groups.

These data come from a statistics article (Rank Analysis of Covariance: Alternative approaches by Andrew Lawson in The Statistician, volume 32 pages 331-337, (1983).) That article argues that a certain statistical test provides support for the belief that the slopes of the liver weights regressed on body weights are statistically significantly different for the 3 treatment groups. Conduct your own analysis and see if you concur or disagree. Hint: appropriate use of indicator variables can be useful for making these comparisons and lend statistical power to your arguments. You also need to deal with at least one really bad outlier. 

Liver_weight	Body_weight	Group
15.96	419	1
13.78	419	1
16.33	438	1
13.25	408	1
14.61	397	1
23.23	580	1
17.74	518	1
16.12	429	1
15.77	464	1
16.84	503	1
28.66	454	2
17.77	453	2
14.55	475	2
15.06	464	2
15.61	474	2
13.27	423	2
13.26	400	2
12.98	428	2
14.93	455	2
16.68	490	2
20.69	557	3
15.39	462	3
14.87	427	3
16.44	438	3
16.66	457	3
15.80	458	3
19.37	528	3
18.27	523	3
19.15	530	3
16.51	516	3