Homework Sourse18 Carotenoids are pigments responsible for much of the red
18. Carotenoids are pigments responsible for much of the red we see in nature. For
example, the bright red beak of the male zebra finch is derived from carotenoids. Carotenoids are also important as antioxidants for humans and other animals, leading a group of researchers to predict that carotenoids in birds may affect immune system function. To test this, a group of zebra finches was randomly divided into two groups (McGraw and Ardia 2003). Ten individual finches received supplemental carotenoids, and 10 individuals did not. All 20 birds were then measured using an assay that measures cell-mediated immunocompetence (PHA) as well as an assay that measures humoral immunity (SRBC). The data are given below. The researchers had independent reasons to believe that neither assay score would be normally distributed, so they preferred a nonparametric test
Treatment
PHA response
SRBC count
CAROT
1.511
2
CAROT
1.311
2
CAROT
1.46
3
CAROT
1.352
4
CAROT
1.491
5
CAROT
1.599
4
CAROT
1.653
8
CAROT
1.39
5
CAROT
1.779
7
CAROT
1.721
4
NO
1.454
4
NO
1.226
2
NO
1.198
3
NO
1.139
4
NO
1.277
3
NO
1.49
0
NO
0.912
3
NO
1.316
4
NO
1.234
2
NO
1.332
1
a. Does PHA differ on average between the birds that received supplemental carotenoids and those that did not?
b. Does SRBC differ on average between the birds that received supplemental carotenoids and those that did not?
c. What assumptions did you require in parts (a) and (b)?
| Treatment | PHA response | SRBC count |
| CAROT | 1.511 | 2 |
| CAROT | 1.311 | 2 |
| CAROT | 1.46 | 3 |
| CAROT | 1.352 | 4 |
| CAROT | 1.491 | 5 |
| CAROT | 1.599 | 4 |
| CAROT | 1.653 | 8 |
| CAROT | 1.39 | 5 |
| CAROT | 1.779 | 7 |
| CAROT | 1.721 | 4 |
| NO | 1.454 | 4 |
| NO | 1.226 | 2 |
| NO | 1.198 | 3 |
| NO | 1.139 | 4 |
| NO | 1.277 | 3 |
| NO | 1.49 | 0 |
| NO | 0.912 | 3 |
| NO | 1.316 | 4 |
| NO | 1.234 | 2 |
| NO | 1.332 | 1 |
Solution
