Hello,

I've successfully implemented 3dlmer for longitudinal models where I've include both an age and age2 term (continuous, quantitative measure) and assessed gender differences (binary 0/1 coding).

3dLMEr -prefix 3dLMEr_age2_gender -jobs 28 \
 -model 'task*age*gender+task*age2*gender+(age|Subj)' \
 -qVars "age,age2" \
 -qVarCenters "0,0" \

An example contrast:

-gltCode  age2.rew-pun.gender   'task : 1*rew -1*pun gender : 1*female -1*male age2 : ' \

I'm curious if I can do a similar analysis, but instead of a binary outcome, if I can use another continuous, quantitative variable (e.g., cortisol values at one time point and/or multiple time points).

For example:

3dLMEr -prefix 3dLMEr_age2_gender -jobs 28 \
 -model 'task*age*cortisol+task*age2*cortisol+(age|Subj)' \
 -qVars "age,age2" \
 -qVarCenters "0,0" \

I tried it with the base model and it ran okay, but when I try to add contrasts that include both continuous quantitative variables, I get this error.

Error in seq.default(2, length(sepTerms), 2) :
  wrong sign in 'by' argument
Calls: process.LME.opts -> gl_Constr -> glfConstr -> seq -> seq.default
In addition: Warning messages:
1: In if (is.na(code[[n]][QVpos + 2])) { :
  the condition has length > 1 and only the first element will be used
2: In if (QVpos == 1) outList[[1]][[n]] <- NA else outList[[1]][[n]] <- glfCons$
  the condition has length > 1 and only the first element will be used
3: In QVpos:(QVpos + 2) :
  numerical expression has 2 elements: only the first used
4: In QVpos:(QVpos + 2) :
  numerical expression has 2 elements: only the first used
Execution halted

I assumed it wouldn't allow me to do this

-gltCode  age2.rew-pun.cort   'task : 1*rew -1*pun cortisol : age2 : ' \

but I thought maybe this would work, but it still doesn't like two quantitative variables in the same contrast

-gltCode  Val_age2med   'task : 1*rew +1*pun cortisol : 5 age2 : 60' \

My guess is that I cannot create a con with both included, without making one of the variables binary, but I wanted to make sure I understand correctly or if there is another way to have a contrast include two quantitative continuous variables.

Other suggestions on how to ask this type of question in this modeling framework?
(edit: question being- do cortisol values moderate longitudinal trajectories in task fMRI patterns of brain activity)


Thanks!!



Edited 1 time(s). Last edit at 01/26/2021 08:10AM by jef.