External Email - Use Caution        

Dear Freesurfer experts,

I have some doubts while running LME analysis on longitudinal data. The main 
goal is to check whether longitudinal BMI scores have any impact on the 
longitudinal cortical thickness changes. The model I’m thinking of is as 
follows:


Y_ij = b0 + b1*time_ij + b2*BMI_ij + b3*Skyra_ij + b4*Prisma_ij + b5*gender_i + 
b6*bslAge_i.


And here is an example design matrix X for the model above:


------------------------------------------

ones|time|BMI |Skyra|Prisma|gender|bslAge|

------------------------------------------

1   |0   |0.62|0    |0     |0     |1.89  |

1   |3.2 |1.56|0    |0     |0     |1.89  |

1   |7.2 |2.04|1    |0     |0     |1.89  |

------------------------------------------

1 |0 |1.1 |0 |0 |1 |1.67 |
1 |1.5 |0.9 |0 |0 |1 |1.67 |
1 |4 |0.9 |1 |0 |1 |1.67 |
1 |5.3 |1.3 |0 |1 |1 |1.67 |

------------------------------------------

1 |0 |0.7 |0 |0 |0 |0.89 |
1 |1.2 |0.5 |0 |0 |0 |0.89 |

------------------------------------------


Note that BMI and bslAge are z-scored, and there are 3 different scanners: 
Avanto (base), Skyra and Prisma. I’m trying to account for differences between 
scanners as well. For some participants, the first two timepoints were scanned 
with one scanner and the last time point with a different one, so it varies 
within the subject. Do I account for the scanner differences in a correct way? 
Should I add interactions with the time variable, as time*Skyra?


Another question. Since BMI is longitudinal, time-variant, should I add an 
interaction with time as well?


Assuming that the above design matrix is “correct”, I would use the following 
contrast [0 0 1 0 0 0 0] to answer my question whether longitudinal BMI scores 
have any impact on longitudinal cortical thickness changes, right?


P.S. I’m running spatiotemporal models with one random effect - intercept.


Thank you for the answer!


Best,

Donatas







_______________________________________________
Freesurfer mailing list
Freesurfer@nmr.mgh.harvard.edu
https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer


The information in this e-mail is intended only for the person to whom it is
addressed. If you believe this e-mail was sent to you in error and the e-mail
contains patient information, please contact the Partners Compliance HelpLine at
http://www.partners.org/complianceline . If the e-mail was sent to you in error
but does not contain patient information, please contact the sender and properly
dispose of the e-mail.

Reply via email to