Decision on T depends on T-1 decision : Time series procedures

Hi ,

I'm trying to model decision making. I believe that decision on instant T dependant on the previous decision on T-1 with the same independants variables.

décision (t) ~ var1(t) + var2(t) + décision (t-1)
I made numerous research on times series. I see that there is lag procedure to be done :

And VAR, Dickey-Fuller, any many others concepts : I do not understand every step.. I believe I'm lost (sorry if it seems basic question) about what I should do in my problem : How to emphasize the influence of T-1 decision on T instant ?

Please find attached data. Really I would appreciate your help.