PSI is unusually focused on the bottom-line impact of its activities. Its philosophy is that although how interventions are done matters, the positive impact they have on the lives of the poor and the vulnerable is more important still. As a result, all interventions are measured and reported — often by a variety of means. At a global level for internal use, PSI measures the number of Disability Adjusted Life Years (DALYs) gained across interventions. DALYs are an internationally accepted measure of health impact and allow disparate interventions to be measured against each other. At the same time, each intervention is assessed independently to estimate how many lives have been saved or improved.