What could be a confounding factor to this issue of drug use?

Question by Mom to be: What could be a confounding factor to this issue of drug use?
Participants: 100 addicts in treatment, 100 non-users
Procedure: Answer 55 survey questions that pertain to parental relationships and background data including previous drug use.
Thoery: Parents influence heroin addiction in their children ealthy childhood.

Best answer:

Answer by billy25685
I believe very few people will tell the truth about their own heroin use. Furthermore the other side of this study is the kids, 50 raised in non-drug using environment and 50 raised in a house with steady use.

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