Let me know if you  notice any serious conflict in this perspective with the definitional criteria mentioned in an earlier slide that quoted the systematic review here Sudhinaraset M, Ingram M, Lofthouse HK, Montagu D (2013) What Is the Role of Informal Healthcare Providers in Developing Countries? A Systematic Review. PLoS ONE 8(2): e54978. doi:10.1371/journal.pone.0054978