Stephen is an applied microeconomist -- a quantitative generalist mostly using unit record (survey and administrative) data, with interests spanning labour and public economics, inequality and poverty, and applied econometrics. Recent research includes work on inequality and poverty, income mobility and poverty dynamics, income volatility, and measurement errors in survey and administrative data. Stephen also has interests in quantitative methods for analysis of income distribution in particular and applied microeconometrics in general, especially survival analysis and statistical graphics.
Stephen is the only person to date to have been President of both of the leading scientific associations in the income distribution field: the International Association for Research on Income and Wealth (IARIW, 2006-8) and Society for the Study of Economic Inequality (ECINEQ, 2021-23). He has also been President of the European Society for Population Economics (ESPE, 1998). Stephen was named as a Distinguished Fellow of the New Zealand Association of Economists in July 2019, and a Fellow of the Royal Economic Society in August 2025.