Hello.  Slope estimates in lme are shrinkage estimates which pull the
OLS slope estimates towards the population estimates, the degree of
which depends on the group sample size and the distance between the
group-based estimate and the overall population estimate.  Although
these shrinkage estimates as said to be more precise with respect to the
true values, they are also biased.  So there is a tradeoff between
precision and bias.

Are there rules of thumb to help determine when it is better to use the
OLS slope estimates and when to use the mixed model (lme) shrinkage
estimates?  I have 35 groups but the numbers per group vary from over 50
to as low as 4.

Thanks for any help.

 

Bill Shipley

Subject Matter Editor, Ecology

North American Editor, Annals of Botany

Département de biologie, Université de Sherbrooke,

Sherbrooke (Québec) J1K 2R1 CANADA

Bill.Shipley@USherbrooke.ca

 <http://callisto.si.usherb.ca:8080/bshipley/>
http://callisto.si.usherb.ca:8080/bshipley/

 


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