What is the test for admitting expert evidence in a sexual assault case?

In R v. DD 2000 SCC 43, Justice Major for the Majority put the issue in that case as follows: This appeal raises the question of whether expert evidence may be admitted to inform the jury that children who have suffered sexual abuse respond in different ways with respect to disclosing the abuse. The expert here did not interview the child, so his evidence was not specific to this complainant, but was a general explanation applicable to all children. - Para. 44.