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the comprehension posttest and the drawing posttest. Students had
20 minutes time for completion, and did not have access to the
science text or their drawings. Finally, students were thanked and
debriefed. As students learned at their own rate, the whole procedure
took about 70–90 minutes, depending on the individual testing
times.
2.4. Results and discussion
2.4.1. Scoring
The dependent variables were students’ scores on the comprehension
and drawing posttests, students’ rating on the mental effort
and the difficulty scales, and the drawing accuracy score indicating
the quality of learner-generated drawings produced by students
in the drawing group during the learning phase.
The comprehension test score (pre- and posttest) for each student
was computed by awarding 1 point for each correct answer, and by
adding up the points to obtain the total comprehension score (out
of a total possible of 25 points). Actual scores ranged from 3 to 24
points, with a mean of 13 points (SD = 5.3). Following Schwamborn
et al. (2010), scoring of the drawing test was carried out by counting
the total number of correct main ideas in each learner’s answer
across the three drawing items. The main ideas were drawn out from
both expert visualizations and a checklist specifying important relational
features. Students could earn a maximum of 19 points on
the drawing test. Two student assistants (teacher trainees in biology)
scored the quality for each of the three drawings for each student
with an acceptable inter-rater agreement of Goodman–Kruskal
gamma of 0.90. Actual scores ranged from 0 to 18.5 points, with a
mean of 7.7 points (SD = 4.7). Total scores of both the comprehension
and the drawing testwere transferred into z-standardized scores
to make them comparable across studies.
The drawing accuracy score (concerning drawing during learning
in the drawing group) was computed by using a coding scheme
adapted fromSchwamborn et al. (2010), which was based on expert
drawings and a checklist specifying important relational features
of the drawings. Students could earn a maximum drawing-accuracy
score of 22 points. Again the two student assistants scored each of
the seven learner-generated drawings for each student with an acceptable
interrater agreement of Goodman–Kruskal gamma of .92.
Both coding schemes were constructed by the first author and a
biology teacher. Actual scores ranged from 4 to 21 points, with a
mean of 13.3 points (SD = 5.0). The total drawing accuracy score was
again transferred into a z-standardized score.
In addition the spatial ability test was scored by tallying the
number correct out of 10, and the motivation questionnaire was
scored by tallying the nine ratings on both subscales to a total score
of motivation. Finally, for comparing performance across the different
tests, the proportion correct on each test was computed by
dividing the student’s obtained score by the total possible score.
2.4.2. Are the groups equivalent on basic characteristics?
Before looking at treatment effects on the dependent variables,
we analyzedwhether the two groups differed on several control variables.
A chi-square analysis indicated that there were no significant
differences regarding gender (p = .562). Separate univariate analyses
of variance (ANOVAs) revealed that the groups did not differ
significantly on age, F < 1; on spatial ability, F < 1; or on motivation,
F(1, 46) = 3.60; p = .064. However, groups differed significantly
on prior knowledge, F(1, 46) = 38.90, p < .001, partial eta2 = .46, in
that students in the drawing group scored significantly lower on
the comprehension pretest (M = .10, SD = .15) than students in the
control group (M = .34, SD = .12). Thus, we included students’ prior
knowledge in the following analyses.
2.4.3. Is there support for the generative drawing effect?
Mean proportion correct and SDs on the comprehension and
drawing posttests for both groups are presented in Table 2. Repeated
measures univariate analyses of variance (ANOVA) with the
comprehension pre- and post-test scores as the within-subject factors
and group (drawing versus control) as the between-subject factor
showed a main effect over time indicating that overall, participants
reached significant knowledge gains between the
comprehension pretest and the comprehension posttest, F(1,
46) = 98.97; p < .001; partial eta2 = .68. An interaction additionally
showed that these knowledge gains were significantly higher for
the drawing group than for the control group, F(1, 46) = 46.17;
p < .001; partial eta2 = .50.
For the drawing test, a repeated measures ANOVA was not possible,
since these items were only used in the posttest. In this case,
a univariate analysis of covariance (ANCOVA) predicting the drawing
test score with group (drawing versus control) as the factorial independent
variable and prior knowledge as a covariate showed that
the drawing group scored significantly better than the control group
on the drawing posttest, F(1, 45) = 13.49, p = .001, partial eta2 = .23.1
Cohen’s d favoring the drawing group over the control group was
0.85 for the comprehension posttest, and 1.15 for the drawing
posttest, all of which are considered large effects. Thus, there is strong
support for the generative drawing effect, as predicted.
Additionally, results revealed that the drawing group needed significantly
more learning time (M = 21.08 min., SD = 4.24) than the
control group (M = 17.38 min., SD = 3.33), F(1, 46) = 11.34, p = .002,
partial eta2 = .20. Thus, to test whether learning time mediates the
positive effect of drawing on text comprehension, additional mediation
analyses (Baron & Kenny, 1986) were calculated by including
learning time as an additional predictor in the aforementioned linear
model. A mediation effect would be detected if, in this case, effects
of drawing on text comprehension would significantly decrease.
Results of the mediation analyses showed that the effect of drawing
on both comprehension test scores and drawing test scores was not
fullymediated by learning time. That is, including learning time still
revealed the interaction between group (drawing versus control)
and time (pre- versus post) in that the drawing group had significantly
higher knowledge gains than the control group on the
comprehension test items (p < .001). Furthermore, the drawing group
also still outperformed the control group on the drawing posttest
after controlling for learning time (p = .009).
Furthermore, results revealed that students in the drawing group
rated their invested mental effort during learning significantly higher
(M = 5.04, SD = 1.12) than students in the control group (M = 3.96,
SD = 1.65), F(1, 46) = 7.05, p = .011, partial eta2 = .13. There was no
difference between the two groups on the perceived difficulty item
(drawing group: M = 4.08, SD = 1.50; control group: M = 4.25,
SD = 1.22; F < 1). Thus, consistent with predictions concerning the
generative drawing effect, t
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