External Email - Use Caution
Dear Freesurfer friends,
It seems that prior messages* on longitudinal recon with missing timepoints have suggested that it is okay for a subset of participants to include different numbers of timepoints into the longitudinal pipeline, so long as there is not a systematic bias (e.g., one group consistently contains more scans than another group, etc.).
Assuming that is still true, I am working with an adolescent dataset from 11 year-olds scanned every 3 months for a year (4 scans total). For participants missing a scan at either timepoint 2 or timepoint 3, I was wondering if creating the BASE/subject-specific template from only three sessions might introduce a temporal bias toward either timepoint 1 (i.e., formed from timepoints 1, 2 & 4), or bias toward timepoint 4 (i.e., formed from timepoint 1, 3 & 4). With consideration to the developmental changes we anticipant measuring over the year, would you be concerned with the potential early vs late skew in the BASE for these missing data cases?
If so, for the missing timepoint participants, I was wondering if I should then avoid generating their subject-specific templates in a way that imposes an even weighting across the three timepoints (i.e., .33 each), and instead adjust the weighting of each timepoint relative to time acquired over the year (e.g., temporal based average), such that timepoint 1 is weighted at .25 and timepoint 2 and 4 are weighted at .375. If this is not a sensible approach, could you please let me know what you think best?
Thank you for your insight!
Much appreciated,
Jacob
* https://secure-web.cisco.com/13XDoOLfZ54QTh8NENJtaYSGUInOnTixvVUeeTP66Z4AcOc...
* https://secure-web.cisco.com/1ivSG2acZebGirLVnyV8qW29ZHDaGha1z3dT3TsM9w986hr...