Current statistics on autism spectrum disorder (ASD) show that boys are nearly five times more likely than girls to have autism. Now a new study proves that in addition to being diagnosed less, girls are also diagnosed at a later age than boys.

The study, conducted by the Kennedy Krieger Institute in in Baltimore, Maryland, analyzed data from the Institute’s Interactive Autism Network (IAN), an online information registry of nearly 50,000 people affected by autism and their families.  Researchers took into account the age that both boys and girls were diagnosed with autism for 9,932 children, and Social Responsiveness Scale data from 5,103 children, which identifies the presence and severity of social impairment.

Results showed that girls with a type of autism called pervasive developmental disorder (PDD)— which is characterized by delays in the development of socialization and communication skills— were diagnosed at an average age of 4 years old, compared to 3.8 years old in boys. In addition to PPD diagnosis, researchers found that Asperger’s syndrome diagnoses also happened later for girls – at 7.6 years old compared to 7.1 years of age for boys.

“The later diagnosis of girls appears to be tied to their areas of delay being less apparent, showing up more as shyness and quietness rather than the more unusual behaviors seen in boys, ” Dr. Paul Lipkin, study author and director of the Interactive Autism Network at Kennedy Krieger told FoxNews.com.

Lipkin said findings suggest that when it comes to social cognition, or the ability to interpret social cues, girls struggle more than boys, while boys have more difficulty with more obvious symptoms like severe mannerisms and repetitive behaviors.

“At the present time, autism screeners are not designed to look at boys and girls differently. This and other studies suggest that such may be needed, particularly around social skill development,” Lipkin said. “So parents, pediatric clinicians, therapists, educators now should give careful consideration to girls who are having difficulties in social situations and assist these girls early.”

Researchers noted an increase in the number of girls diagnosed with autism from 2010-2013 compared to the statistic measured four years earlier. Lipkin said he thinks the reason for the rise might be better public awareness and screening methods.

“We need to look at large groups of girls with autism and better understand their developmental pathways, in order to find the best means for their early identification and to find the best treatments for the challenges they experience,” he said. “One can no longer assume that boys and girls with autism are alike.”

Lipkin said he hopes the findings help change the way autism is diagnosed, and that further research will determine whether less recognizable symptoms in girls are not only leading to later diagnosis, but also under-identification of the condition.

“We need to find the best ways to identify those at both ends of the spectrum, those with severe problems and those with milder problems in social development,” he said. “The quiet girl with social difficulties may have an ASD and may benefit from special treatments aimed at these delays in social development.”

The findings will be presented at the Pediatric Academic Societies annual meeting in San Diego April 28.