In psychological research, one often aims at explaining individual differences in S-R profiles, that
is, individual differences in the responses (R) with which people react to specific stimuli (S). To this
end, researchers often postulate an underlying sequential process, which boils down to the specification
of a set of mediating variables (M) and the processes that link these mediating variables to the stimuli
and responses under study. Obviously, a crucial task is to chart how the individual differences in the S-R
profiles are caused by individual differences in the S-M link and/or by individual differences in the M-R
link. In this paper we propose a new model, called CLASSI, which was explicitly designed for this task.
In particular, the key principle of CLASSI consists of reducing the S, M, and R nodes of a sequential
process to a few mutually exclusive types and inducing an S-M and an M-R person typology from the
data, with the S-M person types being characterized in terms of if S type then M type rules and the M-R
person types in terms of if M type then R type rules. As such, the S-M and M-R person types and their
associated if–then rules represent the important individual differences in the S-M and M-R links of the
sequential process under study. An algorithm to fit the CLASSI model is described and evaluated in a
simulation study. An application of CLASSI to data from the behavioral domain of anger and sadness is
discussed. Finally, we relate CLASSI to other methods and discuss possible extensions.