He is most well known for his international comparative survey research on adolescents and their living and custody arrangements, alcohol consumption and substance abuse.
[1] Bjarnasson has studied adolescent alcohol use and substance abuse, comparing different European countries.
[2][3] In a 2005/06 international comparison of 36 western countries, Bjarnasson studied the proportion of 11-15-year-old children living in different child custody arrangements.
The percent of children living in intact families with both their mother and father was highest in Macedonia (93%), Turkey (89%), Croatia (89%) and Italy (89%), while it was lowest in the United States (60%), Romania (60%), Estonia (66%) and Latvia (67%).
Among the children who did not live with both their parents, the percent in a shared parenting versus sole custody arrangement was highest in Sweden (17%), Iceland (11%), Belgium (11%), Denmark (10%), Italy (9%) and Norway (9%), while it was lowest in Ukraine, Poland, Croatia, Turkey, the Netherlands and Romania, all with 2% or less.