Full interview: As the Labour Party debates the shape of its tax policy in next year's election, and economists keep an eye on the effect of the Government's Investment Boost tax deduction tweaks, Q+A spoke to global expert Michael Keen. . As the former Deputy Director of the Fiscal Affairs Department at the International Monetary Fund, Keen shaped the institution's policies on tax. He praised New Zealand's broad-based GST system and questioned why that same logic didn't apply when discussing the possibility of a Capital Gains Tax. Keen also said the country needed to consider its relatively high corporate tax rate in any discussions about upping productivity. . He also considered people's ideas of a "fair" tax system, and what taxing wealth and multi-national corporations could look like. . Join Jack Tame and the Q+A team and find the answers to the questions that matter. Made with the support of NZ on Air.