Better read the original report by C. D. Howe Institute,
http://www.cdhowe.org/pdf/e-brief_160.pdf
Peter and Marie Thompson are just making ends meet. The married couple in their 30s have two children and live in a rental apartment in Ontario. Peter works full-time and Marie works part-time, together bringing in $40,000 in family income. Marie is considering switching to full-time work to make some extra money. Should she? One factor to consider is whether the extra income will move her to a higher tax bracket. She also has to consider how much of the extra cash she will keep, after her family’s benefits are reduced.
As Marie’s income rises, her family will lose amounts for child tax benefits, the HST refundable credit, and various other provincial and federal cash transfers and credits. For every extra dollar she earns, she might lose up to 68 cents through income taxes and reduced government benefits. Marie’s marginal effective tax rate (METR) in this case would be 68 percent.