Source: https://www.cambridge.org/core/journals/twin-research-and-human-genetics/article/genetic-and-environmental-influences-on-smoking-behavior-across-adolescence-and-young-adulthood-in-the-virginia-twin-study-of-adolescent-behavioral-development-and-the-transitions-to-substance-abuse-followup/E27078A48CA1B20276A6DB2D5D0CAD72