Petty, Sir William (1623-1687), is best remembered as a political economist and a pioneer statistician. He stressed the importance of observation and of numerical measurement of economic matters. He wrote Treatise of Taxes and Contributions (1662-1685) and Political Arithmetic (1683). He was also active in medicine, music, and business. He served as surgeon-general with Oliver Cromwell's army in Ireland, where he became surveyor-general. He was born in Romsey, England, and graduated from Oxford University.