I am trying to compare the accuracy of two different methods of estimating biomass. This data is in the form of percentage cover (and is arcsine transformed). I also have the real biomass values, measured in grams, so three different measurements of the same thing, one of which (for the purpose of the study) I'm assuming provides the correct values, the other two are of unknown accuracy. What's the best way to approach this?
I've tried two separate correlation analyses, and then used Fisher's r-to-z transformation to compare the correlation coefficients.
I was wondering if it's possible to calculate an 'accuracy' value by standardising all the scores, then taking the absolute value of the difference between my (standardised) % cover data points and the (standardised) biomass value in grams. This would be useful because then I could see whether the accuracy changes over time, for example. But does it make sense?
I'm a statistics novice and could really do with some tips! I'm using SPSS.