OK, I know (as Rick pointed out in a recent post) that a lot — maybe too much — of the content on this blog has focused on measurement issues, so I apologize for yet another post on that topic, but this has really been bugging me:
Transparency International has been publishing its well-known and widely-used Corruption Perceptions Index (CPI) since 1995. The index has its pros and cons, several of which have been discussed on this blog (see here, here, here, here, and here). But putting other debates about the CPI’s validity and utility to the side, one thing should be perfectly clear: At least prior to 2012 (when TI changed its method and scoring system for the CPI), a country’s CPI scores CANNOT be compared across years. The fact that Country X scores, say, a 4.4 in 2002, and scores a 4.9 in 2005, does NOT mean that (perceived) corruption has declined in country X. Maybe it did, but it might have stayed the same, or gotten worse. At most, the pre-2012 CPI provides information about country’s ranking relative to other countries, within a single year, with respect to corruption perceptions.
TI itself could not be more explicit about this, stating bluntly “CPI scores before 2012 are not comparable over time.” Yet I keep coming across sources — news articles, presentations by leading international organizations, academic papers — that use year-to-year CPI comparisons to make claims about how corruption in a particular country or region is improving or worsening, or about whether a particular policy intervention is working or not. YOU CAN’T DO THIS! PLEASE STOP!!