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

Question

Quizplus · Accepted Answer

To calculate a 95% confidence interval for the population mean, we use the formula: mean ± (critical value * standard deviation / sqrt(n)), where n is the sample size. Given n=18, mean=11.3, and standard deviation=15.5, and assuming a critical value around 2 for a 95% confidence interval (from the t-distribution table, since the sample size is small and the population standard deviation is unknown), the margin of error is approximately (2 * 15.5 / sqrt(18)). This calculation results in a margin of error close to 7.3, which is rounded or approximated in the options provided. The closest match to our calculation is option C, 11.3 ± 7.7, acknowledging some rounding or approximation in the critical value or in the final calculation.

An Experiment Examined the Impact of THC (The Active Ingredient