An experiment examined the impact of THC (the active ingredient in marijuana) on various physiological and psychological variables.

An experiment examined the impact of THC (the active ingredient in marijuana) on various physiological and psychological variables. The study recruited a sample of 18 young adults who were habitual marijuana smokers. Subjects came to the lab 3 times, each time smoking a different marijuana cigarette: one with 3.9% THC, one with 1.8% THC, and one with no THC (a placebo). The order of the conditions was randomized in a double-blind design.

At the start of each session, no subject reported being "high." After smoking the cigarette, participants rated how "high" they felt, using a positive continuous scale (0 representing not at all "high"). For the placebo condition, participants reported a mean "high" feeling of 11.3, with a standard deviation of 15.5.

A 95% confidence interval for the population mean feeling of "high" after smoking a placebo marijuana cigarette is