); and (3) variations in the quantity of money are often  32  33  Following an approach common to many studies on modern business cycle theory, cross-correlations have been computed on their cyclical component rather than on raw time series.
This choice stems from the need to obtain results that are not affected by components relating to different frequencies, such as seasonality or long-term growth. We use the methodology proposed by M. Baxter and R.G. King in ‘Measuring Business Cycles: Approximate Band-Pass Filters for Economic Time Series’, Review of Economic and Statistics, Vol. 81, No.