  In this paper we consider nonparametric estimation for dependent data, where
the observations do not necessarily come from a linear process. We study
density estimation and also discuss associated problems in nonparametric
regression using the 2-mixing dependence measure. We compare the results under
2-mixing with those derived under the assumption that the process is linear. In
the context of panel time series where one observes data from several
individuals, it is often too strong to assume the joint linearity of processes.
Instead the methods developed in this paper enable us to quantify the
dependence through 2-mixing which allows for nonlinearity. We propose an
estimator of the panel mean function and obtain its rate of convergence. We
show that under certain conditions the rate of convergence can be improved by
allowing the number of individuals in the panel to increase with time.
