As in the case of the Swiss exchange rate, the mere announcement of the OMT led to a rapid convergence of yields and easier financing conditions for banks in stressed countries. Again this effect appeared without any purchases actually undertaken. The effect of balance sheet policies can therefore not be measured by the changes in the size of the balance sheet alone.
The last observation also draws the attention to the importance of expectations about future policy, in particular in periods characterized by high uncertainty. The announcements of the ECB and the SNB removed uncertainty about the future course of policy of the two central banks and stabilized expectations around the outcome desired by policymakers.