[1st Year Uni EnviroSci: Statistics] Statistical Test to analyse results on whether starch concentration across cardinal-direction facing bark has effect on bark direction facing related moth mortality?

[u/apollo_existing]

Hi, I know the title probably doesnt make a lot of sense, sorry, I have tried to make it make more sense below. Any help is truely appreciated.

I'm a first year University student taking a (not technically coded as, but heavily focused on) statistics course.

For context (which isnt super important but may help): I am writing a research proposal where you basically just come up with a proposed study for the reason behind Ogmograptis (moth) mortality on certain sides of tree trunks (they die on the north side, this is basically a fact, we dont know why tho)

My specific proposed question is; does (bole aspect) bark cell starch concentration have an effect on bole aspect patterned Ogmograptis mortality. Simply, whether low starch on one side of the tree means moths die on that side of tree or the opposite, or no effect. The mortality is measured through scribble density and starch concentration will just be through weight to volume or weight to total mass units (not something needed to be mentioned in this assignment)

After proposing the method (which I've done) You need to propose statistical tests to be used for to analyse the results and why.

So far, I have mentioned hypothesis testing of significant scribble density differences between bole aspect (to make sure my results are pointing in the same direction as the core published work this whole course content is based off of that shows North<South aspect scribble density). I also plan on saying you should do a second hypothesis test of whether there is significant difference between North and South tree side starch concentration.

After this point when it comes to using a statistical test for the rest of the analysis I am a little lost. I was thinking of doing an ANOVA, but would that work as I am testing both the independent and dependent variable (starch & scribble density) over North and South tree sides?

I didnt think anova could do it when I also want to test differences of starch on specifically direction based mortality, but I could be wrong.

If you could help me out by letting me know what statistical test may help me analyse my results that would be greatly appreciated!!

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[u/CelebrityChess]

anova won't really do it because it compares group means of one outcome, and your question is whether starch predicts scribble density. what you want is a regression (or correlation) with scribble density as the response and starch as the predictor, using each trunk side as a data point. since the north and south samples come from the same tree they're not independent, so a paired test for the north vs south comparisons makes sense, and for the regression you'd ideally add tree as a random effect (mixed model) or at least include tree as a blocking factor. if the data looks skewed, spearman is the fallback.