Complex sentence: They examined the influence of peer pressure by assessing impact of friends and family on participants' substance use, and reported that people who were encouraged to use substances had a higher usage rate than those who were discouraged.
Split into simpler sentences: They examined the influence of peer pressure by assessing impact of the social network on participants' substance use. The findings confirmed that people who were encouraged by friends and family to use substances had a higher usage rate than those who were discouraged.