The EF Education First English Proficiency Index (EPI), a report which attempts to rank countries by the average level of English language skills amongst adults, has published its latest research on where English is learned around the world and quality of teaching in each country to find the places with the highest proficiency of English as a second language.
The EF EPI sixth edition was calculated using test data from 950,000 test takers in 2015. The test takers were self-selected and no demographic information was collected on them. The tests are used by the company for marketing and placement purposes (Source Wikipedia)
EF EPI Executive Summary (2016):
Spain Country Fact Sheet: