Modelling profit series: nonstationarity and long memory

The dynamic structure of profit rates for 156 US manufacturing companies is analysed by means of fractional integration techniques as an alternative to the commonly used ARIMA models with respect to the 'persistence of profits'. Thereby the pseudo-spectral density aproach of Velasco and Robinson together with model selection criteria is applied. The results show-despite the short lengths of the series and tests for the integer degrees of integration (d = 0, 1)-that 35.5% of the series may be well-approximated by long-range dependent processes, and 54% are nonstationary. This is a confirmation of the strong challenge to the competitive environment hypothesis obtained by previous studies.