  Chaotic dynamics with sensitive dependence on initial conditions may result
in exponential decay of correlation functions. We show that for one-dimensional
interval maps the corresponding quantities, that is, Lyapunov exponents and
exponential decay rates are related. For piecewise linear expanding Markov maps
observed via piecewise analytic functions we provide explicit bounds of the
decay rate in terms of the Lyapunov exponent. In addition, we comment on
similar relations for general piecewise smooth expanding maps.
