[R-sig-ME] Question concerning nlme

Nelson, Gary (FWE ) g@ry@ne|@on @end|ng |rom @t@te@m@@u@
Wed Jul 17 18:54:29 CEST 2019

I work in the field of fisheries. We sample fish using gears that collect individual in clusters, so any analyses done using such sample have to be corrected for intra-cluster correlation.  This has been shown in many papers in my field.

I am trying to compare growth curves between two sexes using the nlme function. The individuals were collected via cluster sampling.  I have been trying to use the nlme function but am having trouble understanding how to specify the correct formulation.

My growth model is:


and I created grouped data with cluster as the grouping variable


and the mixed model I have is


My question is how do I incorporate sexes?  I've tried assuming sex is nested within a cluster where
vbdata<-groupedData(lens~age|cluster/sex,data=catchdata,labels=list(x="age",y="length")) but am unsure if this is correct.

Any help would be appreciated.

<>< <>< <>< <>< <>< <>< <>< <>< <>< <>< <>< <>< <>< <>< <>< <>< <>< <>< <>< <><
Gary A. Nelson, Ph. D
Massachusetts Division of Marine Fisheries
Annisquam River Field Station
30 Emerson Avenue
Gloucester, MA 01930
email: gary.nelson @state.ma.us
phone: 978-282-0308 x114

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