The thesis is organized into three chapters corresponding to three complete articles. In chapter 1, we examine empirical regularities of the main Spanish macroeconomic time series in a way that is comparable across series. Statistics and comovements of the relations between each series and aggregate output are presented from three different perspectives. In chapter 2, we analyse the Phillips relation between inflation and the unemployment rate in Switzerland. We estimate the NAIRU as a parameter that can vary over time. We investigate the precision of these estimates. In chapter 3, we explain Spanish nominal GDP growth for the period 1980-2001, evaluating the various factors involved: changes in domestic output prices, technological change, movements in the terms of trade, and variations in the endowments of labour and capital. Two alternative approaches are used. All empirical results are based on the GDP function approach to model the production sector of an open economy.