We consider the Markov Reference Model (MRM) of program behavior. MRM generates sequences of page requests according to a discrete-time homogeneous Markov chain. We invalidate MRM for instruction traces by means of a cost independent test that is a specialization of the Chi-squared test used in non-parametric statistics. We also find that observed traces have less entropy than MRM traces, which suggests that MRM does not capture the locality and structure of observed traces.