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May 17, 2020 at 17:15 comment added Stochastic I would suggest doing multiple correlation i.e. getting an ANOVA table. When it comes to which variables to exclude, look at the p-values in the ANOVA table. Alternatively you can also use adjusted $R^2$, AIC, BIC or Mallow's Cp for the exclusion of variables. Here are some notes on variable selection.
May 17, 2020 at 16:34 comment added MrUsername12 I have been told to keep using the multivariate model when testing the Hypothesis "The soil being clay or not does not make a difference". When I do this, i still get different answers from the p-value in the ANOVA of the soil column and from using t.test(yield~ soil), but using the t.test function only considers those 2 and not the whole model, so I should use the ANOVA in this case?
May 17, 2020 at 16:19 history edited Stochastic CC BY-SA 4.0
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May 17, 2020 at 16:14 comment added Stochastic Remember it will be different when you model your response (yield) with only one predictor variable. Maybe I was not clear earlier, but for the each variable by itself you will use a t-test while I all are included, you will use a f-test. Sometimes you might find that using a predictor alone to model a response could be significant, but then when fitting it together with other predictors it is not significant at all.
May 17, 2020 at 14:23 comment added MrUsername12 Don't worry, I have solved this part using ANOVA tables I believe. I have updated my question to include another issue I have encountered.
May 16, 2020 at 19:20 comment added Stochastic Firstly, are you using dummy variables for the rainfall? It also depends on how R sees the rainfall variable - is it a factor according to R? You can use just the means and compare them, but I would suggest that you use an ANOVA table since you can set up the hypothesis test then. It would be a more "formal" way of testing for the significance of the rainfall. If you are able to provide some data, I might be able to help more
May 16, 2020 at 17:56 comment added MrUsername12 I am using R. The rainfall is categorised in 3 levels of "None", "Light" and "Heavy" but when I use the t.test it says I need to only have 2 levels of rainfall. Would it suffice to compare each of the means of a specific variety to the rest, or do I need to do it another way like using ANOVA tables? How would I do that?
May 16, 2020 at 11:56 vote accept MrUsername12
May 16, 2020 at 10:25 history answered Stochastic CC BY-SA 4.0