I would like to do a time series analysis to look at the change in environmental sustainability in specific countries, but I am unsure if the data for your 2001 and 2002 ESI is different, or whether the 2002 ESI is just the result of fine-tuning definitions and categories.
In the course of producing the ESI in 2000, 2001, and 2002 we refined the methodology considerably; each new edition of the ESI was different in major ways from its predecessors. Because the methodology differs so much from report to report it is not appropriate to do a time series analysis using the ESI data.