Fig. 2: Study design and data analysis workflow for wearable-based anxiety detection review.

The study design and data analysis workflow consisted of four steps: search and selection of studies, data extraction, feature analysis, and performance analysis. Step 1: Search and selection of studies. a shows the wearable signal modalities analyzed: ECG, RSP, EDA, and PPG. b presents the number of reviewed studies using each signal modality, including single- and multi-modality approaches. Some studies contributed to multiple categories; for example, Jain & Kumar⁴⁴ reported results using ECG alone, EDA alone, and ECG + EDA combined, and were counted in all relevant categories. Step 2: Data extraction. c highlights the elements extracted from each study, including dataset, features, model, validation, and evaluation metrics. Step 3: Feature analysis. d–g summarize the most commonly used features for ECG, RSP, EDA, and PPG, respectively, and their frequencies of use. Step 4: Performance analysis. h displays boxplots illustrating the distribution of accuracy results across different signal modalities, comparing single-modality and multi-modality approaches, while i presents pooled accuracies for single-modality anxiety detection, highlighting the overall performance of ECG, EDA, PPG, and RSP signals. Note: In (b), n refers to the number of independent studies using each signal modality (single- or multi-modality). In d–g, n refers to the number of independent studies that reported the use of each specific feature. In (h), n indicates the number of independent study results contributing to each boxplot. ECG electrocardiogram, EDA electrodermal activity, PPG photoplethysmography, RSP respiratory signal, HR heart rate, SDNN standard deviation of normal-to-normal intervals, RMSSD root mean square of successive differences, HF power high-frequency power, LF power low-frequency power, Mean RR mean R-R interval, Ti/Te inspiratory to expiratory time ratio, IBI inter-breath interval, ReR respiratory rate, SCL skin conductance level, SCR skin conductance response, PPI pulse interval, LF/HF low-frequency to high-frequency power ratio.