Alexander V Lebedev

Questions and Answers (24) View all

• Answer added in Advanced Statistical Analysis
  8 Selecting "candidates" for Latent Variables: linear PLS path modeling setting
  By Alexander Lebedev · University of Bergen
  Alexander Lebedev · University of Bergen

  Thank you very much for your response Tom! This is exactly what I have been looking for. Provided more details in the personal message. 

  Thank you very much for your response Tom! This is exactly what I have been looking for. Provided more details in the personal message.
  Following
• Answer added in Advanced Statistical Analysis
  8 Selecting "candidates" for Latent Variables: linear PLS path modeling setting
  By Alexander Lebedev · University of Bergen
  Alexander Lebedev · University of Bergen

  Hello Tahir, Thank you for your response. I should have clarified this from the very beginning. I am looking for the best strategy to identify candida... [more]

  Hello Tahir, Thank you for your response. I should have clarified this from the very beginning. I am looking for the best strategy to identify candidates to form my LVs (they are going to be reflective constructs). For clinical data, I can use several scales to define one LV (for example, NPId and MADRS depression assessment scales in order to define LV "Depression"). For imaging data this does not seem to be so clear... Because, say, you can define "striatum" as a LV and include caudate nuclei and putamen (neuroanatomically and functionally related brain structures)... But, on the other hand, you can define "strio-pallidar" system as a LV and include caudate, putamen, but also globus pallidus... Therefore, I was wondering whether there are any unbiased solutions for doing this.. Of course, I can try different combinations and afterwards just select the best... But this is a very biased approach, I think..
  Following
• Question asked in Advanced Statistical Analysis
  8 Selecting "candidates" for Latent Variables: linear PLS path modeling setting
  I have just started getting familiar with SEM and am currently playing around with Partial Least Squares (PLS) path modeling. Everything seems to be r... [more]
  I have just started getting familiar with SEM and am currently playing around with Partial Least Squares (PLS) path modeling. Everything seems to be relatively clear so far, except for one thing. I work with neuroimaging data (mainly structural) from patients with neurological disorders. My interest is to model cognitive functions and to estimate an impact of different factors on them (e.g. treatment). Selecting "candidates" for latent variables from high-dimensional clinical data seems relatively straightforward (e.g. use PCA to form "symptom dimensions"), but I'm not sure what to do with imaging data, given the fact that I usually have ~150 regional brain measurements of different modalities. And although I do have some understanding of brain-cognition associations, I'm not 100% sure how to reduce dimensionality in this particular case (merging together some of the anatomically and functionally related brain structures in order to form reflective constructs). My first idea was to perform hierarchial clustering on imaging data using Pearson r^2 as a metric, but then I would be biased towards selection of r^2 cluster-forming threshold. Therefore, maybe it might be better to perform linear modeling first and then select the most significantly correlated structures from GLM results as "candidates" for LVs. Does it make sense? What would you suggest?
  By Alexander Lebedev · University of Bergen
  Following
• Answer added in fMRI
  32 Best stimulus delivery software for fMRI experiments?
  By Alexander Lebedev · University of Bergen
  Alexander Lebedev · University of Bergen

  Dear Colleagues! Thank you very much for sharing your experience. I am currently looking at the PsychoPy. First impressions are very good. I'm almost ... [more]

  Dear Colleagues! Thank you very much for sharing your experience. I am currently looking at the PsychoPy. First impressions are very good. I'm almost sure that after watching youtube tutorial you'll be able to write a simple block design. However, if you are planning to design something a bit more complicated (for instance, if you want to capture and report response time), you'll probably need some coding skills (not much, but preferably in Python). Nevertheless, GUI is pretty intuitive.. I would definitely suggest at least trying it.
  Following
• Answer added in FSL
  7 Do I need to repeat pre-processing for Tracula?
  By Prerona Mukherjee · The University of Edinburgh
  Alexander Lebedev · University of Bergen

  Hi Prerona! I'm afraid that you have to (if you did standard FSL analysis like TBSS), as TRACULA reconstructs tracts using anatomical landmarks derive... [more]

  Hi Prerona! I'm afraid that you have to (if you did standard FSL analysis like TBSS), as TRACULA reconstructs tracts using anatomical landmarks derived from the Freesurfer's output (recon-all).
  Following