Wednesday, January 16, 2008
Cycle plots for time series
In his most recent newsletter, Stephen Few from PerceptualEdge presents a short and interesting article on Cycle Plots (by Naomi Robbins). These are plots for visualizing time series, which enhance both cyclical and trend components of the series. Cycle plots were invented by Cleveland, Dunn, and Terpenning in 1978, and seem quite useful. I have not seen them integrated into any visualization tool, although they definitely are useful and easy to interpret. The closest implementation that I've seen (aside from creating them yourself or using one of the macros suggested in the article) is Spotfire DXP's hierarchies. A hierarchy enables one to define some time scales embedded within other time scales, such as "day within week within month within year". One can then plot the time series at any level of hierarchy, thereby supporting the visualization of trends and cycles at different time scales.