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Clarification on interpreting fixed vs. random effects in GLM modeling with subject effect #12

@yingxuexiao

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@yingxuexiao

Hi ~

Thank you for providing such a useful tool for cell-type proportion estimation and downstream analysis. I have been using scDC(scDC_noclustering) to analyze my single-cell dataset and encountered a question when interpreting the results of the GLM modeling step (fitGLM function).

In your code, it appears that both fixed-effect and random-effect models are fitted when subject_effect = TRUE. However, in my analysis, I consistently observe that the fixed-effect model produces more significant results and is better able to detect changes in major cell types, whereas the random-effect model often yields non-significant p-values, even for cell types with large observed differences.

Given this discrepancy, I would like to ask:

  1. How do you recommend interpreting the results when the fixed and random effect models disagree?

  2. Under what conditions would you suggest using the random-effects results instead of the fixed-effects ones?

  3. Is there a standard way or recommended metric (e.g., subject-level variance or heterogeneity) to decide whether subject_effect should be considered?

I’m currently exploring whether meta-analysis-style heterogeneity metrics (such as I² or variance estimates from random effects) might help guide the model choice, but I would appreciate your guidance on the intended or best-practice usage within the scDC framework.

Thank you for your time and the great work on this package!

Best regards,
Yingxue Xiao

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