“…Nonetheless, in terms of frequency of use, deep learning (convolutional neural network [CNN]) was used in 11 studies, 7 , 20 , 21 , 23 , 24 , 29 , 30 , 31 , 32 , 33 , 34 whilst 6 studies used machine learning. 8 , 22 , 25 , 26 , 27 , 28 The most frequently used subtype of the supervised machine learning approach is the support vector machine, which was used in 4 studies. 25 , 26 , 27 , 28 Three studies used smartphone applications, 14 , 21 , 31 all of which used deep learning techniques.…”