Author contributions: Meng-kan Chen and Hui-Fang Hung had full access to all of the parameters in the study and take responsi- bility for the integrity of the parameters and the accuracy of the parameters analysis. Study concept and design: Hsiu-Hsi Chen. Model construction and collection of parameters from literatures: Meng-kan Chen, Hui-Fang Hung and Amy Ming-fang Yen. Analy- sis and interpretation: Meng-Kan Chen, Hui-Fang Hung, Stephen Duffy, Amy Ming-fang Yen, Hsiu-Hsi Chen. Drafting of the manu- script: Meng-kan Chen, Hui-Fang Hung, Stephen Duffy. Critical revision of the manuscript: Hsiu-Hsi Chen. Statistical analysis: Meng-kan Chen, Hui-Fang Hung and Amy Ming-fang Yen. Study supervision: Hsiu-Hsi Chen.