Hi everyone,
I have a question about calculating r-squared in R. I have tried searching the
archives and couldn't find what I was looking for - but apologies if there is
somewhere I can find this...
I carried out a droughting experiment to test plant competition under limited
water. I had:
- 7 different levels of watering treatment (1 -7 - from most watered to least
watered/)
- 15 replicates at each level.
Soil moisture readings were taken 4 times throughout the experiment (so I have
105 readings for each of the 4 times) and I now want to check that there was a
significant decrease in soil moisture as I decreased the watering frequency,
i.e. watering level 7 showed lower soil moisture units than level 1.
I have carried out a repeated measures anova as follows (where block is which
time the reading was taken: 1,2,3 or 4):
model1<-aov(soilmoisture~wateringlevel+Error(block/wateringlevel))
I then plotted (soilmoisture~wateringlevel) and fitted a regression line:
lm1<-lm(soilmoisture~wateringlevel)
abline(lm1,lty=1)
Here are my questions:
1) Is the repeated measures anova I have entered correct to tell me if
there is a significant difference in my watering levels?
2) How do I calculate r2 value to show much variation my watering
level explains? - and then put this figure on my plot?
Thank you - and again apologies if this is a too-basic question - (I am a real
stats and R beginner).
Please let me know if I need to provide any more detail!
Sarah
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