The three main methods are as follows: the tissue composition-based algorithm (TCB) (also called as mechanistic model of tissue binding), which is based on drug binding to tissue components , the correlation-based algorithm (CBA), which uses a specific tissue to find the Kp values for other tissues based on a regression equation using the Kp value of the muscle , and a nonlinear regression model using machine learning algorithm for Kp value prediction. The study by Yun et al. was the first to employ machine learning (ML) to predict Kp values . Recently, our group developed a more accurate multimodal model using the minimum required experimental values and physicochemical descriptors [root-mean-square error (RMSE) and % of two-fold error: 0.39 and 64.5% in 10-fold cross-validation] :34). Therefore, we believed that missing data may worsen the accuracy of the QSAR model.