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Although there is a growing literature examining the benefits of
mindfulness meditation (Harp et al., 2022; Howarth et al., 2019; Ito
et al., 2022), some scholars argue that there are limitations to this research
(Van Dam et al., 2018). Notably, these scientists suggest that some past
work on mindfulness has been conducted without adequate rigor (e.g.,
failure to use adequate control conditions). Based on these limitations,
imagine that we wanted to conduct a study to test this question: Does
mindfulness meditation effectively reduce college students’ stress?
How should we design such a study? An important consideration to
start with is which type of study design is best: repeated measures or
between subjects? In Chapter 9, we learned about the repeated-measures
study design, which is essentially a before and after type of study. We
measure each participant before our intervention and again afterwards.
So, one option would be to measure the stress levels of our participants,
have them engage in mindfulness meditation, and then measure their
stress levels again. Although this option would be okay, as we learned in
the last chapter, this type of design is prone to participant effects. Our
participants may want to feel lower stress, and so they may look for ways
in which the mindfulness meditation helped them. Given this potential
drawback, we probably shouldn’t choose the repeated-measures design.
independent groups Instead, we may want to go with an independent groups design
design (also called a (also called a between-subjects design), which is a type of study where
between-subjects design) different groups of participants experience the different levels of the
a type of study where independent variable. Thus, in this type of design, we would have
different groups of one group of participants undergo mindfulness meditation, while a
participants experience second group of different participants serves as our control condition.
the different levels of the In general, we are much less likely to observe participant effects in
independent variable.
independent groups designs, because participants in one condition
don’t know what participants in the other condition are doing. Thus,
it is more difficult for them to guess what the study is about overall.
Because we have different people in our two conditions, we need to
use the t-test for independent samples that we learned about in the
first half of this chapter.
Here in the Statistics for Research section, we’re going to focus more
on the type of research design that a t-test for independent means
analyzes, discuss the assumptions for running this test (and how to
test them), and how to determine confidence intervals and effect sizes
with the t-test for independent means.

Where Do the Data come From?
To conduct our study of mindfulness meditation, we decide
to have participants in the mindfulness condition watch a
30-minute video each day for one month. In the video, an
expert therapist guides participants through a mindfulness exercise.

362 S TATIS TI c S F OR R ESEAR c H

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