# Using Explainable AI (XAI) for the Prediction of Falls in the Older Population
## 3 Results
### SHAP Values  
A summary and the bar plots containing the top 20 features of the highest mean absolute SHAP values for each model are presented in Figures 1-8. The SHAP value summary plot shows the spread of every SHAP value that was calculated for every feature in each sample. The colour of the plots represents the feature value, with '1' being represented as red and '0' represented being blue for the binary variables. For age, the colour changes from blue to red with an increasing feature value. The summary plot visualises the distribution of the SHAP values for each feature whilst ranking the feature according to the mean absolute SHAP values. Alternatively, this can be observed in the bar plot, which provides a comparison of the mean absolute SHAP values of the top 20 features.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Complex Falls Top Features** & **Feature Importance** \\ \hline Fall in last year & 0.135 \\ Age & 0.110 \\ Afraid of fall & 0.081 \\ Osteoporosis & 0.045 \\ Sex & 0.042 \\ Grip weakness & 0.039 \\ Osteoarthritis & 0.034 \\ Unsteady getting up from chair & 0.034 \\ Urine incontinence & 0.028 \\ Frequent fainter when young & 0.028 \\ Hypertension & 0.023 \\ Polypharmacy & 0.023 \\ Feels unsteady on standing & 0.022 \\ Antidepressants & 0.021 \\ Antihypertensives & 0.020 \\ Anticholinergies & 0.019 \\ Psychiatric problems & 0.019 \\ Abnormal heart rhythm & 0.017 \\ History of blackout/faint & 0.016 \\ Diabetes & 0.016 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Top 20 features (by feature importance coefficient) in the complex falls model.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Syncope Model** & **Feature Importance** \\ \hline Age & 0.118 \\ Frequent fainter when young & 0.043 \\ Polypharmacy & 0.041 \\ Fall in last year & 0.040 \\ MI & 0.039 \\ Unsteady getting up from chair & 0.038 \\ Sex & 0.033 \\ Osteoporosis & 0.031 \\ Angina & 0.030 \\ Grip weakness & 0.029 \\ Abnormal heart rhythm & 0.029 \\ Antihypertensives & 0.029 \\ Varicose ulcers & 0.027 \\ Cancer & 0.027 \\ Osteoarthritis & 0.026 \\ Afraid of fall & 0.025 \\ Hypertension & 0.024 \\ Urine incontinence & 0.023 \\ Poor smell & 0.022 \\ History of blackout/faint & 0.021 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Top 20 features (by feature importance coefficient) in the syncope model.  
Figure 1: All falls and syncope SHAP summary plot. Fall in the last year is at the top of the y axis, which is followed by sex (female = red; male = blue) and being afraid of falling. This suggests that a fall in the last year has, amongst the other features, the biggest contribution towards the prediction of a future fall (all falls and syncope). Within each feature, every point across the x axis represents the SHAP value of the feature for each participant. As observed, a fall in the last year contributes positively towards a future fall, and most positively in some participants, compared to other features, but the wide distribution of the points suggests the variability of this positive contribution amongst participants. In comparison, not falling in the last year has a more consistent contribution towards having no future fall prediction. The only two dichotomous features whose presence has negative contributions to the model are being a frequent fainter when they were young, and more notably, having chronic obstructive pulmonary disease (COPD). In regards age, higher values tend to contribute positively to the model, with the opposite being generally true, but with there being a degree of heterogeneity (i.e., some red dots can be seen as having a negative impact and some blue dots have a positive impact).  
Figure 3: Simple falls SHAP summary plot.  
Figure 2: All falls and syncope SHAP bar plot.  
Figure 4: Simple falls SHAP bar plot.  
Figure 5: Complex falls SHAP summary plot.  
Figure 6: Complex falls SHAP bar plot.  
Figure 7: Syncope SHAP summary plot.