In this contribution, variance properties of L-2 model reduction are studied. That is, given an estimated model of high order we study the resulting variance of an L-2 reduced approximation. The main result of the paper is showing that estimating a low-order output error (OE) model via L-2 model reduction of a high-order model gives a smaller variance compared to estimating a low-order model directly from data in case of undermodeling. This has previously been shown to hold for Finite Impulse Response models, but is in this paper extended to general linear OE models. (C) 2003 Elsevier Ltd. All rights reserved.