title: Standardisation in MuMIn package in R
body: <p>I am using the 'MuMIn' package in R to select models and calculate effect sizes of the input variables (rain, brk, onset, wid). To make my effect size comparable between variables, I standardised them using standardize function in <code>arm</code> package. Here is the code that I am following:</p>
  
  <p>For reference, please refer to the appendix of this paper: <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1420-9101.2010.02210.x/full" rel="nofollow">http://onlinelibrary.wiley.com/doi/10.1111/j.1420-9101.2010.02210.x/full</a>
  Grueber et al. 2011: Multimodel inference in ecology and evolution: challenges and solutions</p>
  
  <pre><code>data1&lt;-read.csv("data.csv",header=TRUE)       #reads the data
  
  global.model&lt;-lmer(yld.res ~ rain + brk + onset + wid + (1|state),data=data1,REML="FALSE")               # prepares a global model
  
  stdz.model &lt;- standardize(global.model,standardize.y = FALSE)          # standardise the input varaibles 
  
  model.set &lt;- dredge(stdz.model)      ### generates the full submodel set
  
  top.models &lt;- get.models(model.set, subset= delta&lt;2)   # selects models with delta AIC &lt;2
  
  model.avg(top.models)       # calculates the average effect size of input variables
  </code></pre>
  
  <p>Here is the result of <code>model.avg(top.models)</code> which gives the average effect size of each input variable</p>
  
  <pre><code>Coefficients: 
           (Intercept)     brk         rain         wid        onset
  subset -4.281975e-14   -106.0919   51.54688    39.82837    35.68766
  </code></pre>
  
  <p>I read around how the standardize function works- subtracts mean and divides by 2SD.  </p>
  
  <p>My question is this: Since I have standardised the input variables, should not the effect sizes be between -1 to 1? or the effect size which the output shows is correct?</p>
  
  <p>Please advise</p>
  
  <p>Thanks a lot</p>