... of health system performance has been criticized for not using appropriate method of transformation and the z-scores transformation has been recommended (SPRG, 2001). For time – dependent ... way to prize the most performing countries and penalize the less performing ones. An advantage of this transformation is that, using the same percentile transformation for different years, any ... total exports. Therefore, to avoid adding up apples and pears, before going to the aggregation stage it is necessary to bring the indicators to the same standard, by transforming them in pure,...