ageism cost the united states $63 billion in one year according to a yale school of public health study. in a unfpa report about aging in the 21st century, it highlighted the need to "develop a new rights-based culture of ageing and a change of mindset and societal attitudes towards ageing and older persons, from welfare recipients to active, contributing members of society". unfpa said that this "requires, among others, working towards the development of international human rights instruments and their translation into national laws and regulations and affirmative measures that challenge age discrimination and recognise older people as autonomous subjects". older people's music participation contributes to the maintenance of interpersonal relationships and promoting successful aging. at the same time, older persons can make contributions to society including caregiving and volunteering. for example, "a study of bolivian migrants who [had] moved to spain found that 69% left their children at home, usually with grandparents. in rural china, grandparents care for 38% of children aged under five whose parents have gone to work in cities."