You'd like to smooth data in a time series.
Use Excel's exponential smoothing feature in the Analysis ToolPak or construct a smoothed data series yourself using spreadsheet functions and VBA.
Smoothing data is often desirable to remove unwanted noise in a data series. Computing moving averages as discussed in Recipe 6.3 is actually a smoothing process. Besides the moving averages methods discussed earlier, there are other ways to smooth data. Excel offers an exponential smoothing feature as part of the Analysis ToolPak. Further, you can construct any smoothing operations you desire using standard spreadsheet functions (and/or VBA). You already saw this approach in the previous recipe; however, this time I'll show you how to use a weighted moving average that makes use of a cubic spline interpolation kernel.
Exponential smoothing is also a weighted-averaging technique. The idea behind weighted averaging is to give data values closest to the value being forecast or estimated greater importance, or influence, as opposed to values further away. Exponential smoothing uses the following formula:
F n +1 is the value being estimated at time interval n + 1. α is a weighting factor, which is called a damping factor in Excel. F n is the previous estimated value, and Y n is the previous actual value ...