## 3 Materials and Methods
### The Modified DE Algorithm
The results of the experiments conducted on real patients' data demonstrate that the method is feasible and accurate. We find that the conjunctive belief rule base CDSS is more effective than the disjunctive one. The conjunctive belief rule base CDSS achieved accuracy, sensitivity, and specificity of 0.954, 0.923, and 0.959, respectively, which is significantly higher than the traditional machine learning approaches. In future, other factors that may influence the clinical severity prediction of COVID-19 can be addressed. Moreover, other optimization algorithms and even hybridization of them as well as other dataset can be explored. Federated learning in COVID-19 severity prediction can be addressed also for preserving the privacy of the patients. Furthermore, we have a plan to extend the proposed CDSS for other diseases that people will have to face as the result of viruses' mutations. Further research can be done to make the system more versatile so that it can predict the COVID-19 severity for different nationalities having different immune systems. F.A. : conceptualization, data curation, methodology, validation, visualization, software, formal analysis, writing--original draft preparation, resources; M.S.H. : supervision, methodology, investigation, validation, project administration, writing--review and editing; R.U.I. : supervision, investigation, validation, writing--review; K.A. : supervision, investigation, validation, resources, project administration, writing--review and editing, funding acquisition. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. Data Availability Statement: Data set used in this study is available on request from the corresponding author. The authors declare no conflict of interest. Figure 6: Comparision of BRBES (T-CBRB) with traditional machine learning algorithms. ## Abbreviations

The following abbreviations are used in this manuscript: \begin{tabular}{l l} BRBES & Belief Rule-Based Expert System \\ CBRB & Conjunctive Belief Rule Base \\ DBRB & Disjunctive Belief Rule Base \\ CDSS & Clinical Decision Support System \\ DE & Differential Evolution \\ SVM & Support Vector Machine \\ DT & Decision Tree \\ ANN & Artificial Neural Network \\ LR & Logistic Regression \\ \end{tabular} 

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