The analysis of indexed astronomical time series - III. Intrinsic period scatter

Three tests for the presence of intrinsic scatter (as distinct from extrinsic measurement error) in the periods of long-period pulsating stars are described. Real and simulated data are analysed for illustrative purposes. Modifications demanded by the possibility of trends in the underlying mean period are given. A method for establishing the detailed properties of the intrinsic period scatter is discussed. The wider applicability of some of the techniques is demonstrated by an analysis of short-period variable star data.