Some types of restricted and repetitive behaviors become more prevalent among autistic children and teenagers over time, depending on their age and intellectual ability, whereas others decrease, two new studies show.

The results lend fresh support to the argument that restricted and repetitive behaviors — a core diagnostic trait that includes repetitive movements, insistence on sameness, sensory sensitivities and restricted interests — are too diverse to be lumped together.

“This is a complex behavioral domain that comprises several different subdomains that likely have different causes and might respond to different treatments,” says Mirko Uljarević, senior research fellow at the University of Melbourne in Victoria, Australia, who led one of the studies.