Moreover, twin studies showed that it is much more likely that identical twins are both on the autism spectrum than that non-identical twins are both on the autism spectrum. Identical twins have nearly the same DNA. Therefore, it is highly probable that they are either both autistic or both not autistic. Non-identical twins share only half of their genes which makes it less likely that they both have the disorder. Scientists have shown that the recurrence risk (the likelihood that a child is on the autism spectrum if it has a sister or a brother that is autistic as well) is 20 to 80 times higher than the probability for having the disorder in the average population.