["The Economic History Review, EarlyView. ", "\nAbstract\nUsing existing and new price data sets, we provide the first estimates of market integration across England over the entire 200 years of the industrial revolution. We document a significant, though not huge, integration improvement for markets furthest from London. Full integration was achieved by the 1830s. Our price data sets vary in quality (type of average, price rounding, frequency of stale prices). We show that this severely biases some standard statistical tests of market integration, and we develop and implement new techniques to ensure valid inference. We discuss the application of these techniques to other historical data sets.\n"]