The answer? Yep!

A study published this summer showed the impact of cannabis on people’s ability to drive safely in a driving simulator. The study provides a great opportunity to practice basic experimental designs. The original study appears in JAMA Network Open, and it was summarized in a variety of online popular sources. I’ll be quoting from the New York Post.

Here’s the introduction and description of the study, as described by the Post.

A new study warns that driving after eating cannabis edibles can significantly impair road performance and reaction times, even if blood tests show THC levels far below the legal limit.

Researchers found that drivers who consumed higher doses of edible THC struggled with lane control, had slower reaction times and experienced greater speed fluctuations. Yet, their blood tests stayed below the standard legal cutoff used to prove impairment at roadside traffic stops.

To assess how oral cannabis impacts driving, researchers at the Centre for Addiction and Mental Health in Toronto conducted a trial with 40 healthy adult volunteers who regularly use cannabis.

Each participant attended four separate sessions [on four separate days] in which they consumed soft-chew gummies containing either 0, 2, 10 or 20 milligrams of THC.

The researchers then tested the drivers using a driving simulator at two, five and 24 hours after consumption, tracking how well drivers stayed in their lane, how quickly they reacted to road events and how consistently they maintained their speed.

Blood samples and self-reported ratings of intoxication were also collected.

The results showed driving impairment at two and five hours after consuming 10- and 20-milligram gummies. Compared with placebo, participants who consumed those doses had greater variability in lane position, while the 20-milligram dose was also linked to slower reaction times and less consistent speed control.

a) Complete the table below, by identifying the major variables in the study. Here’s a hint: There was at least one primary IV and five DVs!

Variable name	Levels of this variable	IV? DV?	If it’s an IV, was it independent-groups or within-groups?

b) What kind of experiment was this? Choices: posttest only, pretest/posttest, repeated measures, concurrent measures. Explain your answer.

c) If you read the empirical journal article, you’ll see that the researchers counterbalanced the four doses of THC. Why did they need to do this? Which of the four big validities is this choice relevant for?

d) Sketch a line or bar graph showing the result for “variability in lane position” after 2 hours of exposure.

e) Sketch a line or bar graph showing the result for “reaction time” after 2 hours of exposure. (hint: when it comes to driving reaction time, shorter is generally better!)

f) Comment on the external validity of this study; specifically, do you think people’s behavior in the driving simulator will generalize to driving in the real-world? Why or why not?

g) Does this study change your own thinking about the safety of driving after consuming cannabis gummies?