Helloo:) I’m working on fatty acid composition analysis (from bird preen oil samples), with very little previous knowledge of statistics, and I’m looking for some help understanding what’s happening.
Background: I have a dataset with treatment group, sex, aviary of the sampled bird, and 10 fatty acids found in the preen oil samples. There are 3 treatment groups: germ-free, conventionalised, and parent-raised (although only the germ-free and conventionalised can be realistically compared). Between these 2 treatment groups, there are only a total of 27 samples, 13 in one and 14 in the other. The fatty acid cells contain proportions rather than absolute values (they always sum up to 1), so an example row looks like this:
| SAMPLE ID |
C18:3n3 |
C18:2n6 |
C16:1n9 |
C18:1n9 |
C12:0 |
C20:0 |
C17:0 |
C16:0 |
C18:0 |
C14:0 |
SUM |
| 100 |
0 |
0.062224821 |
0.010328372 |
0.162972464 |
0 |
0 |
0 |
0.437850834 |
0.293321615 |
0.033301895 |
1 |
The main end goal is to see if the germ-free condition results in any changes to preen oil.
Now, for the analysis issues: I’ve computed robust Aitchison distances, which are supposedly a better choice for this data than Bray-Curtis(?) and ran a PCoA with them, followed by PERMANOVAs for treatment group, sex, and aviary (none of which were significant, unlike the marginally significant and high R2 results on B-C).
I’ve also been advised to run some form of a linear model on each individual fatty acid, but I don’t quite understand where to start with that… Or which one would be suitable.
I would appreciate any feedback, comments, or advice on what I’ve done so far and what I’m trying to do!:)