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* Analysis: Electrolyte imbalances are common in critically ill patients and
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can be exacerbated by sepsis.
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can be exacerbated by sepsis.
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Analysis of the Results
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1. Combined Dataset: The top 6 features are all demographic or administrative
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data (ICULOS, HospAdmTime, Unit1/2, Gender, Age). The first clinical
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measurements (Platelets, Fibrinogen, etc.) appear further down the list with
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significantly lower importance scores.
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2. Non-Sepsis Only Dataset: The results are remarkably similar to the combined
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dataset. The same top 6 demographic/administrative features dominate, and the
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clinical variables have comparable, relatively low scores.
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3. Sepsis-Only Dataset: This is where things get interesting.
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* The same demographic/administrative features are still at the top, but
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their importance scores are drastically lower (e.g., HospAdmTime drops
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from ~0.55 to ~0.34, and Age from ~0.22 to ~0.09).
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* More importantly, a much wider range of clinical variables now appear in
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the list with non-trivial importance scores (e.g., Platelets, Phosphate,
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Resp, HR, etc.). In the combined and non-sepsis datasets, many of these
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clinical features had scores so low they didn't even make the list.
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The Problem
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The strong predictive power of the demographic and administrative features in the combined dataset is masking the importance of the clinical variables.
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Here's a breakdown of why this is happening:
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* Confounding Variables: The demographic and administrative data (ICULOS,
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HospAdmTime, etc.) are likely strong confounders. They are correlated with
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both the clinical measurements and the outcome (sepsis). For example, a
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patient who has been in the ICU for a long time (ICULOS) is more likely to
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have both more clinical measurements taken and a higher chance of developing
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sepsis.
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* Data Imbalance: With a 93% to 7% ratio, the model is heavily biased towards the
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non-sepsis cases. The features that are good at predicting "not sepsis" will
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dominate the feature selection process. Since the non-sepsis group is so large,
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the model learns that the demographic data is a very good predictor for the
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majority of the data.
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* Masking Effect: Because the MRMR algorithm is trying to find a balance between
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relevance to the target and redundancy with other features, the strong,
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universally present demographic features get picked first. Once they are in the
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model, they "explain away" a lot of the variance, leaving less for the
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clinical variables to contribute, thus lowering their apparent importance.
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What Happens When You Separate the Datasets?
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* Non-Sepsis: When you run MRMR on only the non-sepsis data, the situation is
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largely the same as the combined set. The demographic features are still the
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best predictors for this large, relatively homogeneous group.
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*
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* Sepsis: When you isolate the sepsis cases, you remove the overwhelming
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influence of the non-sepsis group. In this context, the model is forced to look
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for the subtle patterns within the sepsis patients. This is where the clinical
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variables (HR, Resp, WBC, etc.) become much more important, as they are the
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indicators that change as the condition progresses. The demographic data is
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still relevant, but its predictive power is diminished relative to the
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