Researchers examined 100 people suffering from herniated disks in their backs. Five of them were found to have a defect in a particular gene. The researchers also examined 100 people who had no problems with the disks in their backs; none had the genetic defect. They concluded that the genetic defect increases the likelihood of herniated disks.
The statement 'When the researchers examined the family of one of the subjects who did not suffer from herniated disks, they found 30 family members who did not have the defective gene, and 20 of them suffered from herniated disks' most strengthens the researchers' reasoning.