The clustering of errors on real channels seriously complicates the task of evaluating the performance of error-control techniques. A model is introduced that, in addition to having the ability to match error distributions, greatly simplifies the task of code evaluations. Having selected the parameters of the model by matching the statistics recorded by Townsend and Watts on the switched telephone network, the model is shown to predict the results of tests of an interleaved burst-error-correcting code. The utility of the model is demonstrated in the analysis of error-detection codes with delayed retransmissions.