It’s not an index based on just asking people their feelings - it’s based on indices like quality of health care, crime rate, housing etc. We know suicide rates are higher in more open countries , since in more repressed societies suicides are less likely to be reported as such - they are more likely to be recorded as “ accidental deaths” as there is more stigma attached to suicide in say, Catholic countries. So the statistics give a distorted picture. So, countries like Denmark have a more accurate picture of actual suicides. U.K. has more overcrowding, poorer housing, increasing inequality etc so will fall down the list.