Periodic properties of interpolated time series

Although linearly interpolated series are often used in economics, little has been done to examine the effects of interpolation on time-series properties and on statistical inference. We show that linear interpolation of a trend stationary series superimposes a 'periodic' structure on the moments of the series. Using conventional time-series methods to make inference about the interpolated series may therefore be invalid. Also, the interpolated series may exhibit more shock persistence than the original trend stationary series.