In one massive experiment, potentially delinquent boys were assigned to a 5-year treatment program that included professional counseling and family assistance. many years later, joan mccord's investigation of this program's effectiveness revealed that

The investigation revealed that clients' accounts of the program's effectiveness were often misleading and overly positive.

This happen because the effectiveness measurement from the organization that created the program was very biased.

For example, they often measure the change in routine that shown after following the program, but that change in routine could easily reverted back as soon as the program is over.