# In many studies the hierarchy of evaluation system and

Above definition implies that PF-573228 the grey absolute correlation degrees between indicators are based on the summary of differences among all nn samples. Pairwise comparison of all initial indicators yields the grey correlation matrix:equation(3)

Notice that matrix CC is a symmetric matrix with diagonal entries εii=1εii=1. Therefore, we only consider the upper right triangle in the rest of paper. We can set a reference threshold 0?ε∗?10?ε∗?1. If εij?ε∗εij?ε∗, indicators Ii0 and Ij0 can be said to belong to the same class. Then we can design a new indicator or just choose a typical indicator from the cluster, denoted as IiIi, to represent the class. Repeat cytoxic T cells step until all elements in matrix CC finish the pairwise comparison. Finally, a new simplified set of safety evaluation indicators can be obtained, denoted as I= I1,I2,…Ik I= I1,I2,…Ik . Due to the powerful correlation analysis capability of grey relational clustering method, simplified II can better avoid the multicollinearity and over-reliance on similar indicators in evaluation, and therefore increase the effectiveness and reliability of the AHP-based methodology which will be described in following sections.