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I am working on a binary classification model (healthy/diseased) based on gene expression data of different patients. As a second task, I would like to stratify these patients and find subgroups. I expect that the summary pattern of different genes within an experiment will be the strongest predictor of the outcome (differential coexpression analysis). How do I deal with the importance of the group-setup in my ML model if I need to follow the rule not to include IDs (in my case experiment IDs) in a model?

Also, I have repeated measures of the same patients and also hope for significant differences between some patient groups - does that mean I should just include the patient IDs as well, or pre-define some groups, or use all patient characteristics that could be interesting as features?

This is how my data is currently organized:

experiment ID gene expression patient ID label
1 A 11 1234 healthy
1 B 5 1234 healthy
2 A 3 4356 diseased
2 B 9 4356 diseased
3 A 13 1234 healthy
3 B 6 1234 healthy
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  • $\begingroup$ Welcome to DataScienceSE. As far as I understand you have to do some feature engineering: if you provide the data like this with the patient id, the model might just use the patient id as feature, i.e. "if id == 1234 then healthy". Also the model wouldn't be able to use any relation between gene A and B here (not sure if this is on purpose?). At first sight it looks like it would make more sense to have one instance for one patient, with feature 1 = expresson for gene A and feature 2 = expression for gene B. $\endgroup$
    – Erwan
    Oct 25, 2021 at 23:21
  • $\begingroup$ Thank you, @Erwan! I would definitely like to use the relation between the expression of different genes, this is what I am trying to include in my design somehow. Doesn't the "experiment ID" function as a grouping variable that makes it possible? Is changing the format to "wide" the best way to achieve a gene expression pattern recognition? $\endgroup$
    – vhio
    Oct 27, 2021 at 12:48
  • $\begingroup$ EDIT: I have up to 30 different genes. Also, it's not straightforward to use one instance for one patient, as I sometimes have repeated measures for patients, as shown. I could use one instance for one experiment I guess? $\endgroup$
    – vhio
    Oct 27, 2021 at 12:54

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I started writing this as a comment but I realized that I have too many things to say... I'm not sure that it's a proper answer either but hopefully it's useful:

  • I'm not really sure that I understand what the "experiment id" represents here, but this idea of relying on it as a grouping variable doesn't seem very good to me: it's going to be used by the model as a potential explanatory variable for the target, I'm not sure that's what you want here.
  • I would definitely advise to format all the observations for one patient as one instance. The model assumes that the instances are independent of each other, so it cannot use the relation between two instances which share a patient id.
  • 30 different genes as features could be perfectly fine, but it depends how many instances you have as training data. Too few instances and/or too many features could cause overfitting, i.e. the model using details which happen by chance in the data as patterns. Anyway there are some options for this kind of problem, feature selection would be the most obvious one.
  • For the repeated measures for one patient, assuming the measures always include all/most of the genes, this is not necessarily a problem: the different sets of measures can be used as different instances. However in this case there might be some bias in the distribution, for example if multiple measures are more common with healthy patients. A workaround would be to always include N instances for every patient, and if needed repeat the same measures if the patient doesn't have several sets of measures.
  • About the different patients groups: my first intuition would be to simply train a different model for every group, this way you can observe how the models (or their predictions) differ.
  • If the goal is to find the most important causative factors, I'd recommend training a simple decision tree model: decision trees are easily observable and interpretable, with the most discriminative features at the top/root of the tree. Don't hesitate to restrict the parameters, in particular the depth of the tree, in order to make the result readable.
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  • $\begingroup$ Very useful tips, thanks! I didn't mention another variable which is the "condition": the expression value of all these genes is analyzed under 4 different conditions. If I change the format to "wide" (one patient -> one instance), the feature count would be further multiplied by 4 and they would be like "condition1/gene1", "condition1/gene2", and so on. Is there a nicer way to solve this? $\endgroup$
    – vhio
    Oct 28, 2021 at 16:36
  • $\begingroup$ @vhio I don't understand what this "condition" represents exactly, but it looks like maybe it could be another feature, e.g. an instance would be represented as condition, gene1, gene2, .... If a patient has multiple conditions these would be in different instances. $\endgroup$
    – Erwan
    Oct 29, 2021 at 11:46

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