© 2010 The Authors Fiscal Studies © 2010 Institute for Fiscal Studies. Published by Blackwell Publishing Ltd, 9600 Garsington Road, Oxford, OX4 2DQ, UK, and 350 Main Street, Malden, MA 02148, USA. The UK National Minimum Wage in Retrospect PETER DOLTON, CHIARA ROSAZZA BONDIBENE and JONATHAN WADSWORTH APPENDIX A. ROBUSTNESS CHECKS Table A1. Incremental differences-in-differences wage inequality estimates (including proportion of workers in the manufacturing sector, as a control for industry) 50:5 ratio 50:10 ratio Total Total Total Total 16–retirement 16–retirement 16–retirement 16–retirement 406 areas 140 areas 406 areas 140 areas NMW 0.092** 0.096** 0.054** 0.061** base period (0.006) (0.010) (0.005) (0.007) NMW*1999 -0.035** -0.051** -0.008 -0.006 (0.008) (0.012) (0.006) (0.009) NMW*2000 -0.053** -0.051** -0.027** -0.029** (0.007) (0.010) (0.006) (0.009) NMW*2001 -0.057** -0.061** -0.031** -0.043** (0.007) (0.011) (0.006) (0.009) NMW*2002 -0.067** -0.080** -0.032** -0.049** (0.008) (0.012) (0.006) (0.010) NMW*2003 -0.062** -0.065** -0.036** -0.042** (0.007) (0.011) (0.006) (0.009) NMW*2004 -0.068** -0.074** -0.043** -0.050** (0.007) (0.011) (0.005) (0.008) NMW*2005 -0.091** -0.095** -0.054** -0.053** (0.007) (0.012) (0.006) (0.009) NMW*2006 -0.076** -0.098** -0.046** -0.057** (0.008) (0.012) (0.006) (0.010) NMW*2007 -0.102** -0.116** -0.064** -0.077** (0.007) (0.013) (0.006) (0.011) ** significant at 5 per cent level. * significant at 10 per cent level. Notes: All regressions contain year dummies, area fixed effects and within-area time-varying controls. Heteroscedasticity autocorrelation (HAC) robust standard errors are given in parentheses. The NMW variable is the proportion of employees in each area paid at or below the national minimum wage (Share).