If output gaps in a currency union are not sufficiently coherent, the common monetary policy will not be optimal for all countries or regions in the union. It is common practice to measure coherence of output gaps by a correlation coefficient. We propose new measures of output gap coherence, which take differences in the signs and/or amplitudes of the output gaps more adequately into account than the correlation coefficient. We apply these measures to the euro area, using the US as a benchmark. We also examine how sensitive our findings are to different ways of calculating the output gaps.

We investigate the causal relationship between public debt ratios and economic growth rates for 31 EU and OECD countries. We estimate a panel VAR model that incorporates the long-term real interest rate on government bonds as a vehicle to transmit shocks in both the public debt to GDP ratio and the economic growth rate. We find no causal link from public debt to growth, irrespective of the levels of the public debt ratio. Rather, we find a causal relationship from growth to public debt. In high-debt countries, the direct negative impact of growth on public debt is enhanced by an increase in the long-term real interest rate, which in its turn decreases interest-sensitive demand and leads to a further increase in the public debt ratio.