A lot of people believe that using marijuana can make them more creative–some artists use it specifically when they are composing songs, painting, or creating new work.
A recent study experimentally tested this idea. The study provides a useful example of a null effect. Here is a summary by a journalist in the Washington Post.
The journalist writes:
...researchers designed a randomized controlled trial comparing the creative outputs of light cannabis users who had just imbibed vs. those who had not.
In a first set of experiments, about 107 light users of cannabis were asked to take a standard creativity test within 15 minutes of getting high. For the control group, the researchers asked 84 other participants to do the task only if they had not used cannabis in the past 12 hours, by when any effects would have worn off.
For the creativity test, the participants were asked to consider a brick, and generate as many creative uses as possible for it in four minutes. As expected, participants who were under the influence felt more jovial, which made them feel like their ideas were more creative than sober participants.
But creativity assessments by third-party raters, who did not know who was under the influence, were a buzzkill. When they rated the responses on novelty and usefulness, they did not see a difference in creativity.
Questions
a) Start by making a table of the variables in this study.
| Variable name | What are the variable's possible levels? | Is this manipulated or measured? | Is this an IV or a DV? | For IVs: is it within groups or independent groups? |
b) Check your work above. There were two operationalizations of the dependent variable, creativity. Do you have both of them? Do you also have the dependent variable of joviality?
c) Was this study an experiment or a correlational study? How do you know?
d) Which kind of experiment is this? Posttest only? Pretest/posttest? Concurrent measures? Repeated measures?
e) Sketch two graphs of the study's results: One graph for each dependent variable. (Hint: The x-axis will show the same independent variable in both graphs).
f) The results which showed that, when creativity was measured by third-party raters, there was no effect of using cannabis on creativity. This is a "null effect" as introduced in Chapter 11. Flip to Table 11.3 in your text: we'll apply several of the questions to this study.
- Could there have been an ineffective manipulation of the IV?
- Is there evidence of a ceiling or floor effect on the IV or DV?
(Hint: the fact that there were differences in joviality and self-reported creativity suggest that the IV actually did work–right?) - What are some potential causes of within-groups variability in this study? How might the researchers have minimized their effects? Consider situation noise, measurement error, and individual differences.