As most people who follow this blog are likely aware, Transparency International released the 2015 Corruption Perceptions Index (CPI) last week. There is, of course, a lot to talk about here, and I’m sure many commentators and scholars will spend a lot of time poring over the new data and debating its significance. Given my previous criticisms of the CPI’s suggestion that scores for the same country can be compared across time (see here, here, here, and here), that was naturally the first thing I focused on. I was hoping that TI might take up some version of my suggestion to report statistical confidence intervals in an easy-to-see place in the main data table, or, even better, test for statistically significant changes in scores across years. Alas, TI didn’t do either of those things. (The confidence intervals are still available, but you have to download the data to find them.) TI did, however, report that since 2012, some countries had improved, while others had deteriorated. In particular, TI noted three countries (Greece, Senegal, and the UK) had improved their CPI scores since 2012, while five countries (Australia, Brazil, Libya, Spain, and Turkey) had seen a notable worsening.
Because of last year’s fiasco with China (where TI emphasized a decline in China’s CPI score that turned out to be bogus), I was initially skeptical. So, I went ahead and implemented the procedure that I outlined in my post from a few months ago to see whether, for these eight countries, there really was a genuine, statistically meaningful change in the CPI score. I was pleasantly surprised to discover that in all eight of the countries that TI identified, the change in the CPI score between 2012 and 2015 was indeed statistically significant at conventional levels, and do not seem to have been driven by the addition or subtraction of sources in the later year, or by a large anomalous jump in a single source. (Though it’s perhaps worth noting that in the case of Brazil – which TI particularly emphasizes in its press release – the change is just barely significant at conventional levels, and of the seven sources used to construct the score, although four indicate moderate to large declines, two show no change and one actually rates Brazil as improving slightly from 2012 to 2015.) So, while I still have a number of criticisms (about which more below), I’ll gladly give credit where credit is due: In this year’s publicity materials, TI has indeed identified countries where there is statistically significant change in CPI scores, generally driven by changes in several of the underlying data sources. I hope that in future years, TI will go further (and save me some time) by simply including in the main data table not only the confidence interval for the current year, but also a simple three-category indicator (up, down, null) for whether there has been a statistically significant change in the CPI in the past three years. (This is important because of the way the CPI is covered by mainstream journalists: Though researchers might dig into the data tables, most journalists or casual readers just look for year-to-year changes.)
Now, I did say I still had some concerns, so in the interest of continued constructive engagement, let me lay out why I still don’t think we should treat within-country year-to-year changes in CPI scores as terribly meaningful: Continue reading