Variations in sampling time, or sampling jitter, is a common insidious industrial control problem. This work investigates how the stochastic sampling jitter adversely affects the performance of control loops using control performance assessment (CPA) tools. It is analytically shown that sampling jitter may both improve or deteriorate the control performance, and through simulation, it is demonstrated that the estimates of Harris index from the time invariant ARMA model are reliable, provided the sampling jitter is relatively small. Furthermore we propose a method to analyze the effects of sampling jitter, when the jitter is unknown and not directly measurable. From the simulations of 15 typical processes, it is shown that the proposed method is reliable for most of the investigated cases. (C) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.