  In the paper, we introduce a new measure of correlation between possibly
non-stationary series. As the measure is based on the detrending moving-average
cross-correlation analysis (DMCA), we label it as the DMCA coefficient
$\rho_{DMCA}(\lambda)$ with a moving average window length $\lambda$. We
analytically show that the coefficient ranges between -1 and 1 as a standard
correlation does. In the simulation study, we show that the values of
$\rho_{DMCA}(\lambda)$ very well correspond to the true correlation between the
analyzed series regardless the (non-)stationarity level. Dependence of the
newly proposed measure on other parameters -- correlation level, moving average
window length and time series length -- is discussed as well.
