Hi, I have a Community (COM) composed of 6 species: A, B, C, D, E & F. The density of my Community is thus (Eq.1): dCOM = dA + dB + dC + dE + dF
I would like to calculate and plot a linear regression between the density of each of my species and the density of the whole community (illustrating how the density of each species varies with variations of the whole community). For example, I would like to plot dA = a * dCOM + b, with a and b the slope and intercept of the regression. The problem is that dA and dCOM are correlated because dA contributes to values of dCOM (see Eq.1 above), and thus I'm probably not allowed to use a "simple" linear regression (because parametric statistics do not allow for correlated observations). >From what I red (eg, www.ats.ucla.edu/stat/r/faq/spatial_regression.htm), Linear Mixed Models allow for correlated observations by adding a correction to the values. The webpage also says that we can use the correlation option in the lme function (nlme package) to find the type of correction to be used, but I can’t figure out how to do this for my dataset. Can someone help me please ? You will find an example of my dataset below (density of species A [dA] and density of the whole community [dCOM]) and my R script. Example from my dataset: dA dCOM 0.611 0.73 0.474 0.669 0.203 0.388 0.011 0.213 0.407 0.722 0.148 0.437 0.084 0.281 0 0.054 0.402 0.93 0.044 0.285 0.011 0.147 0 0.091 0.547 0.767 0.559 0.699 0.321 0.441 0.084 0.262 0.428 0.761 0.234 0.398 0.019 0.191 0 0.053 0.302 0.509 0.06 0.213 0.045 0.184 0.033 0.118 0.374 0.585 0.256 0.5 0.22 0.401 0.136 0.275 0.503 0.684 0.48 0.617 0.257 0.387 0.038 0.159 0.382 0.611 0.192 0.393 0.047 0.243 0.036 0.188 R script for this example: dummy <- rep(1,36) # grouping variable in our data model1 <- lme(fixed = dA ~ dCOM, data = bb1, random = ~ 1 | dCOM/dummy, correlation= ?,method = "ML") Thank you very much. Julie. -- View this message in context: http://r.789695.n4.nabble.com/Calculating-plotting-a-linear-regression-between-two-correlated-variables-tp4319051p4319051.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
