300 • PART iii: YogA foR EduCATing foR SElf-REgulATion And EngAgEMEnT
outcome issues, studies presorting insufficient data, and studies that were not randomized
controlled trials. These exclusions from the aggregate analysis highlight the importance
of commitment to a high-quality research design—studies with poorer designs simply do
not have the impact. Ultimately, the review was based on nine studies, with seven stud-
ies depicted in the plot of general effect size in the selected studies (Ferreira-Vorkapic
et al., 2015).
Ferreira-Vorkapic et al. (2015) completed an effect size analysis on the remaining studies,
through standardized mean difference and Hedges’s g, which allowed for the comparison
of experimental conditions. Although these studies all evaluated yoga in schools, they were
very different in several ways. The studies included either elementary school, middle school,
or high school students. The types of yoga utilized included Vinayasa, Ashtanga, Yoga Ed,
Kripalu Yoga, Niroga, Mindful Girls Yoga, and Hatha Yoga. The dosage of yoga ranged from
10 to 18 weeks, 15 to 90 minutes per session, and 1 to 5 times a week. Control groups varied
as well. Five of the studies used an active control group (i.e., physical education or physical
activity) and the other studies used a waitlist or no inventions (Ferreira-Vorkapic et al., 2015).
The general plot of the outcomes shows divided results with half of the studies favor-
ing yoga and the other half favoring controls. In aggregate, the overall effect for yoga was
not found to be significant. Appropriately, the authors state, “This is probably due to the
heterogeneity of the variables” (Ferreira-Vorkapic et al., 2015, p. 3). To illustrate issues at
hand, one of the studies that favored the controls was Haden, Daly, and Hagins (2014). This
study compared 15 students in yoga to 15 students in physical education. The yoga group
comprised 10 males and five females; the physical education group comprised seven males
and eight females. The yoga group engaged in 15 weeks of Ashtanga Yoga (90 minutes a
session), three times a week. At the end of the study, there were no significant effects on
behavior, aggression, and self-perception but there was an increased negative affect for the
yoga group.
There several issues that should be noted to provide context for the Haden et al. (2014)
study. First, the sample size was very small, too small to look at gender effects. That leads
to the second issue: There is emerging evidence that when middle and high school age male
students are assigned to yoga over physical education, they frequently indicate that they
feel they are missing out and would prefer the competitive and more vigorous activity in
physical education class. We saw this trend in a qualitative study we conducted recently.
Once students reached fifth and sixth grades, male students began to voice a preference for
physical education over yoga. In discussion on strategies to negotiate this, researchers have
argued for research designs that do not make students select yoga or physical education.
When putting yoga up against soccer for a 13-year-old male, often soccer wins. That makes
sense and it is not what we are trying to study. In this case, we end up with adolescent males
filling out the posttest surveys, upset that they had to do yoga and missed soccer, football,
track, and weight lifting for 15 weeks. Rather, active control groups should offer noncompet-
itive activities with similar physical exertion levels. Next, another issue that needs further
exploration is the reporting of increased negative affect at posttest among those in the yoga
group. Although this might be explained as an expression of the disappointment and frus-
tration resulting from 15 weeks of missing sports, researchers are beginning to look more
deeply into this phenomenon. It is hypothesized that the increased awareness of body and
feeling states that occurs in yoga practice may make students aware of feelings that they had
not noticed prior. More research is needed to better understand this process as well as how
to assess more specifically exactly what is occurring.