We consider an autoregressive moving-average (ARMA) time series where the observations are perturbed by two kinds of outliers: an additive outlier (AO) or an innovation outlier (IO). Abraham and Yatawara [Journal of Time Series Analysis (1988) Vol. 9, pp. 109-19] investigate a sequential test which successively detects and identifies the outlier type. In this article, we propose an extension of this test, called 'modified sequential test', which performs the two procedures simultaneously and coherently. The asymptotic distribution of the test statistic is calculated under the null hypothesis that no outlier is present. Comparison of the two test procedures using simulation experiments shows that the proposed test gives a better power especially in the case of an IO. Copyright 2008 The Author. Journal compilation 2008 Blackwell Publishing Ltd
