1. Azevedo, V.: Aging of the Portuguese population will only end in 2049. http://expresso.sapo.pt/sociedade/2017-03-29-Envelhecimento-da-populacao-portuguesa-so-vai-parar-em-2049 . (in Portuguese)
2. PORDATA: Contemporary Portugal Database, Fundação Francisco Manuel dos Santos. http://www.pordata.pt/Portugal/Indicadores+de+envelhecimento-526
3. World Health Organization (2014). http://www.un.org/apps/news/story.asp?NewsID=49275#.WSmZIju4KON
4. Marktest: Study Telecommunications Barometer (2016). http://www.marktest.com/wap/a/n/id~2046.aspx
5. Gartner (2016). http://www.gartner.com/newsroom/id/3323017