ICT Development Index (IDI) is a composite index that combines 11 indicators into one benchmark measure. It is used to monitor and compare developments in Information and communication Technology (ICT) between countries and over time. 

Methodology: The IDI is divided into the following three sub-Indices, and a total of 11 indicators:

1. Access sub-index: This sub-index captures ICT readiness and includes Five infrastructure and access indicators:
   • Fixed-telefone subscriptions per 100 inhabitants
   • Mobile-cellular telephone subscriptions per 100 inhabitants
   • International internet bandwith (bit/s) per Internet user
   • Percentage of households with a computer
   • Percentage of households with Internet access
2. Use sub-index: This sub-index captures ICT intensity and includes three intensity and usage indicators:
   • Percentage of individuals using the internet
   • Fixed-broadband subscriptions per 100 inhabitants
   • Active mobile-broadband subscriptions per 100 inhabitants
3. Skills sub-index: This sub-index seeks to capture capabilities or skills which are important for ICTs. It includes three proxy indicators (since these are merely proxys, the skills sub-index is given less weight in the computation than the other two sub-indices:
   • Mean years of schooling
   • Secondary gross enrolment ratio
   • Tertiary gross enrolment ratio

Source: The International Telecommunications Union (ITU) presents the index annually in their "Measuring the Information Society Report". Please refer to their website for a more detailed description of the methodology.