Questions to be addressed
This case study involves the use of mixed models of fixed and random effects and addresses a number of questions.
What is a mixed model?
How does one use REML to fit a mixed model and how can one interpret the output?
Finally, having fitted the model how can one deduce whether there are significant random effects of ram and ewe on offspring weaning weight?
-
In addressing these questions the case study first considers
the statistical model with just the fixed effects developed
in Case Study 3 and compares the outputs obtained by the conventional method of general least squares with that using REML.
- The case study then
dwells at some length on the meaning of a mixed model, how
it can incorporate units of observation at different layers
and how the data structure framework can be diagrammatically
sketched in the form of a ´mixed model tree´.
- Finally, having fitted
the mixed model, the case study describes how to interpret
the findings.
|