Parameters for Trafo Electrical Insulation

There are many parameter influence the condition assesment of Trafo Insulation. Here I make them become several, they are Furfural content, Oil tan delta, water content,acidity, breakdown voltage, IFT,CO2 content, and based on Total Combustible Gas (TCG) condition.

Can somebody suggest me, how to evaluate the priority of the parameter ?, how can i make the weigthing factor of that parameter above? ] what parameter is the most important and less ?

thanks