Machine learning integration in microRNA-based markers for cardiovascular diseases: A systematic review

Table 4 Risk-of-bias assessment using QUADAS-2 domains

Ref.	Patient selection (risk of bias/applicability)	Index test (including feature selection and overfitting risk)	Reference standard	Flow and timing (including external validation)	Overall ML-specific concerns
Kayvanpour et al[8], 2021	Low/Low	Low (10-fold CV was reported, but feature-selection timing was not fully clear)	Low (diagnosis strictly adjudicated by a board of 3 expert cardiologists using ESC guidelines)	Low (internal CV only; no external)	Moderate overfitting risk due to no external validation
Ren et al[13], 2024	Unclear/Low	Low (LASSO/SCAD used for selection; validation on matched sample)	Unclear	High (no formal validation split reported)	Limited validation; ML mainly for feature identification
Samadishadlou et al[14], 2023	Low/Low	Low (7:3 split and 10-fold CV)	Unclear	Low (internal only)	Small test set; class imbalance addressed using sample weighting
Samadishadlou et al[15], 2024	Low/Low	Low (LASSO and 5/10-fold CV)	Unclear	Low (internal and independent test set)	Improved validation compared to prior work
Reel et al[16], 2025	Low/Low	Low (8:2 split and balanced accuracy metric)	Unclear	Low (internal only)	Use of balanced accuracy helps with potential imbalance
Sajid et al[17], 2024	Low/Low	Low (8:2 and 10-fold CV and hold-out)	Unclear	Low (internal only)	Ensemble methods; good internal practices
Yerukala Sathipati et al[18], 2025	Unclear/Low (small n = 15)	Low (8:2 split)	Unclear	Low (external validation performed via independent GEO dataset)	Very small sample; high risk of overfitting
Jusic et al[19], 2023	Low/Low	Low (8:2 and 10-fold CV)	Unclear	Low (internal only)	Small cohort
Errington et al[20], 2021	Low/Low	Low (10-fold CV and external datasets)	Unclear	Low (external validation performed)	Strongest validation approach among included studies

CV: Cross validation; ML: Machine learning; ESC: European society of cardiology; LASSO: Least absolute shrinkage and selection operator; SCAD: Smoothly clipped absolute deviation; GEO: Gene Expression Omnibus.