Hi,

I'm having a lot of trouble figuring out how to answer this question so if anyone can help by showing me step by step instructions on how to get the answer I'll be extremely happy and will offer 50fg (sorry I'd give all of it away but this is only question 1 of the assignment and I don't know if I'll end up needing help with the other questions too )

this is question 1 of my assignment:
Q1) Does the “size” of galled goldenrods differ in any (meaningful) way from non-galled
goldenrods?

Using the data collected on your pairs of parasitized and unparasitized goldenrods
in your own sample, perform a Principle Component Analysis using the following
variables: i) the total height of the goldenrod plant (to the closest cm). ii) the height
of the lowest leaf on the goldenrod, iii) the diameter of the stem 2 cm from the
ground (to the closest mm) and iv) the diameter of the stem 3 cm below the base of
the gall (to the closest mm) on the parasitized goldenrod.

Retain a sufficient number of PC’s that explain a “meaningful” (as determined by
you) amount of the total variation in your data set. Describe your new ordination
system via the interpretation of loadings.

Using your re-scored variables as the response variables compare the mean (or
median*) heights of pairs of parasitized and unparasitized goldenrods in your
sample. *Please use the appropriate statistical test(s) for the above analyses, and
indicate in your report why the test(s) you used were appropriate.

Produce a boxplot illustrating the difference in “size” of the pairs of unparasitized
and parasitized goldenrods.


SO FAR:
I went straight into performing a principle component analysis of these variables and got the loadings for them . am I supposed to be performing tests before using princomp? are there assumptions that I should be checking first?
After running PCA, I found that the sufficient number of PCs that I need to retain are the first 3 components. and then I described what the variance is most affected by for each of those components. does this answer the question (describe your new ordination system via the interpretation of loadings)?

If someone could tell me whether I'm doing this correctly so far that would be great.
now I'm supposed to use my re-scored variables as the response variables to compare the mean or median heights of pairs of parasitized and unparasitized goldenrods. I'm not sure how to do this but I figured I should start by checking normality of each component (components 1, 2, and 3), and then check normality of plant height with galls, and plant height without.
the next thing I did was do a var.test between the two : >var.test(g.plant.height,plant.height).
am I doing this right? I'm not entirely sure what my prof means by this entire part "using your re-scored variables...."

any help will be much appreciated, please I've been working on this for an entire week and I'm still on the first question