Statistical inference in multi-state coherent systems

My research area is Reliability Theory. Currently, I have been working on research problems that deal with Multi-state coherent systems. These systems are such that their components and systems themselves can be in one of (M + 1) possible states 0, 1, 2, • • • , M at any given time, where the extreme states 0 and M represent completely failed and completely working states respectively, and others are intermediate states that decrease in performance level as the system or a component makes a transition from state i to (i − 1), i = M, (M − 1), • • • , 1.