New research from the University of Ulster confirms that girls are made of sugar and spice and everything nice. Tony Cassidy, the lead researcher on the project, found sisters make their siblings more optimistic and help families deal with problems in emotionally healthy ways. Families with at least one sister are more cohesive and communicate more often. Girls who grow up with a sister are more independent and achieve more than girls who have brothers. Cassidy surveyed 571 young adults between 17 and 25. He found that sisters have the most positive impact on broken families. Only children scored in the mid-range for happiness while boys who had only brothers were the least happy.