Hi Bronwyn, 

I think years-between-scans should be years-from-baseline-scans . You may need to compute that if what you have is really years between neighbouring scans.

1. Usually people use intercept and maybe years-from-baseline as random effects. I would not include too many random effects, as it each adds a lot of free parameters and you need a lot of data to fit all that in a meaningful way. Which of your columns are random effects can be passed lme_fit_FS(X,[1 2],Y(:,1)+Y(:,2),ni);
for example has column 1 and 2 as random effects. 

2. You can do a model comparison as described on our wiki 
https://surfer.nmr.mgh.harvard.edu/fswiki/LinearMixedEffectsModels 

You run the more complex model first (do the EM init and maybe RgGrow and RgW fit) and then the simple one (only the EMinit and  RgW fit) and do a likelihodd ratio test.  An example is on the above wiki.

Best ,Martin 





On 27 Feb 2017, at 04:16, Bronwyn Overs <b.overs@neura.edu.au> wrote:

Dear mailing list,

I am trying to run a LME model using the matlab tools, but I’m unsure how to specify the model we wish to run. We have a qdec file that contains the following columns:
fsid, fsid-abse, years between scans, age at baseline, gender, group

We want to specify a model where we can examine four interaction terms (years*age, years*group, age*group, years*age*group), as well as random effects for the intercept, years and age. My questions are:
1. How do we specify a model that will include the random effects we want?
2. How do we compare our full model (3 random effects) with a model excluding the random effect for age?

Kind regards,

Bronwyn Overs
Research Assistant

Neuroscience Research Australia
Margarete Ainsworth Building
Barker Street Randwick Sydney NSW 2031 Australia
M 0411 308 769 T +61 2 9399 1883 F +61 2 9399 1265


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