  We present a detailed analysis of two-state trajectories obtained from
force-clamp spectroscopy (FCS) of reversibly bonded systems. FCS offers the
unique possibility to vary the equilibrium constant in two-state kinetics, for
instance the unfolding and refolding of biomolecules, over many orders of
magnitude due to the force dependency of the respective rates. We discuss two
different kinds of counting statistics, the event-counting usually employed in
the statistical analysis of two-state kinetics and additionally the so-called
cycle-counting. While in the former case all transitions are counted,
cycle-counting means that we focus on one type of transitions. This might be
advantageous in particular if the equilibrium constant is much larger or much
smaller than unity because in these situations the temporal resolution of the
experimental setup might not allow to capture all transitions of an
event-counting analysis. We discuss how an analysis of FCS data for complex
systems exhibiting dynamic disorder might be performed yielding information
about the detailed force-dependence of the transition rates and about the time
scale of the dynamic disorder. In addition, the question as to which extent the
kinetic scheme can be viewed as a Markovian two-state model is discussed.
