The IDI was initially developed in 1998, then revised in 2003 and again in 2010. We currently use version 5, which has been in place since 2019. However, the changes between 2010 and 2019 were to the IDI Profile Reports and our systems, rather than to the IDI assessment itself. This article (available on our website) describes the development of the IDI.
You can also read about subsequent validation studies of the IDI in the following articles: