; and (ii) the use of scientific methods rules out, to the extent possible, alternative explanations for the documented change. (B) Scientific methods For the purposes of subparagraph (A) , the term scientific methods means— (i) evaluation by an experimental trial, in which participants are randomly assigned to participate in the practice that is subject to such trial; or (ii) evaluation by a quasi-experimental trial, in which the outcomes for participants are compared with outcomes for a control group that is made up of individuals who are similar to such participants. (5) Intervention The term intervention means the provision of programs and services that are supported by research, are evidence-based or promising practices, and are provided to youth who are involved in, or who are identified by evidence-based risk assessment methods as being at high risk of continued involvement in, juvenile delinquency or criminal street gangs, as a result of indications that demonstrate involvement with problems such as truancy, substance abuse, mental health treatment needs, or siblings who have had involvement with juvenile or criminal justice systems. (6) Juvenile delinquency and criminal street gang activity prevention The term juvenile delinquency and criminal street gang activity prevention means the provision of programs and resources to children and families who have not yet had substantial contact with criminal justice or juvenile justice systems, that— (A) are designed to reduce potential juvenile delinquency and criminal street gang activity risks