Over the last two decades long memory time series have become an
established modeling tool in many areas of science and technology,
including geosciences, medical sciences, telecommunication networks
and to some extend financial econometrics. It has however been
recently realized that practically all statistical procedures
intended to detect and estimate long memory give spurious results if
a time series without long memory is perturbed by nonstationarities,
like trends or breaks (change-points). For example, if a mean of a
short memory time series changes, a test for the presence of long
memory will incorrectly indicate that the time series has long
memory. Similarly, a test for the presence of change point, will
incorectly show that that a change point is present if the time
series is stationary with long memory. A growing body of research
which has accumulated over the last decade is concerned with finding
and illustrating cases of such spurious inference, without
addressing the issue how to choose between the two modeling
approaches. In this talk we will discuss two new statistical tests
aimed at distinguishing between the two approaches and apply them to
a financial and a hydrological time series. The talk will focus on
the ideas rather than technicalities and will be broadly accessible.