An exuberant history instructor, seeing the positive
effect of SI on students' grades during the previous semester, challenged the
premise that student participation in Supplemental Instruction (SI) must be
voluntary. The instructor posited that if it worked for some students, it may
work for many and approached the campus learning center with the idea of
devoting an hour of her class time each week to SI. This study is a result of
her efforts to support her students' academic success.
The Traditional SI
Supplemental Instruction, developed by researchers in 1973 at the
University of Missouri-Kansas City (UMKC), is a structured form of peer teaching
in which students voluntarily seek academic support from peers to increase their
academic performance in a difficult class. Peer teaching, incidentally, had its
beginning in the great city states of Greece, where Aristotle is reported to
have used "archons or student leaders who took care of the many details for him"
(Wagner, 1982, p. 8). In SI, the peer teacher, called the "SI leader," is
usually an undergraduate student who was successful in the course and was
recommended by a faculty member to lead weekly review sessions. The SI leader
collaborates with the instructor, attends course lectures, takes notes,
completes assigned readings, and then schedules three or four 50-minute SI
sessions each week at times convenient to the majority of the students in the
course (Blanc, DeBuhr, & Martin, 1983). The SI leader is specifically
trained in proactive learning and study strategies and is considered the
facilitator of the group, not a mini-professor. His or her role is to provide
structure to the study session, not to relecture or introduce new material
(Arendale, 1994). SI is designed to assist students in mastering course concepts
and to increase students' competency in reading, reasoning, and study skills
(Blanc et al., 1983).
The SI model was developed in response to the high
attrition rates occurring at UMKC. In 1981, the SI program won certification by
the United States Department of Education (USDOE) as an Exemplary Educational
Program. SI is one of two programs certified by USDOE as both increasing college
student academic achievement and graduation rates. With this award, SI became
eligible for funds from the National Diffusion Network (Widmar, 1994). According
to the Center for Supplemental Instruction (2000), educators from UMKC have
trained learning assistance personnel and faculty using the SI model from more
than 900 colleges and universities in the United States and 12 other
Arendale (1994) described SI as avoiding the remedial stigma
often attached to academic assistance programs because it identifies high-risk
courses rather than high-risk students. High-risk courses, as defined by UMKC,
have 30% of students earning Ds, Fs, or Ws. Student attendance in SI is
voluntary and open to everyone in the targeted course.
So why challenge the premise that SI attendance
be voluntary, especially with the success educators are experiencing with the
current SI model (Anker, 1991; Blanc, et al., 1983; Kochenour, Jolley, Kaup,
Patrick, Roach, & Wenzler, 1997; Romoser, Rich, Williford, & Kousaleous,
1997)? Trends in help-seeking research suggest that some students do not seek
out academic assistance or voluntarily participate as readily as others,
particularly low achieving students. In one study, the rate of help-seeking was
low for students making high grades and low grades; however, help-seeking
increased among students making average grades (Karabenick & Knapp, 1988).
This study was consistent with Rosen (1983), who reported that help-seeking was
curvilinear, that is, higher when the need was moderate and lower when the need
was either very high or very low. Freidlander (1980) also indicated that less
than 25% of low ability students in a special admissions program sought
assistance from academic-related support programs and that continuing students
were more likely to utilize these services than first-time freshmen.
educators have tried incentives to encourage students to attend academic support
programs, but these methods, based on several research studies, have received
mixed results. Reittinger and Palmer (1996) found that offering extra course
credit for a psychology course by requiring students to attend 90% of the
scheduled SI sessions resulted in less than 10% of the students choosing to
attend SI. Allen, Kolpas, and Stathis (1992) investigated mandatory versus
voluntary SI attendance for Calculus I classes at a community college. Students
in the mandatory classes received a 10% increase in their grade as a reward for
participating in SI. Final course grades for the mandatory group were 20% higher
than the voluntary SI group. In a second experiment, instructors integrated SI
strategies into Calculus I classes. Comparisons of students' grades were made to
regular Calculus I classes; students in the modified sections earned a mean
final course grade of nearly a letter grade higher than students in the regular
In another study (Hodges, 1997), attendance in SI was
unaffected when high-risk students were exposed to weekly verbal prompts and
required to self-monitor their SI attendance for extra credit. Participants in
the treatment group were compared to high-risk students not receiving the
treatment, and no significant difference in attendance was found between the
groups. However, students who did attend SI were more successful in the targeted
courses than non-SI attendees. Webster and Dee (in press) reported similar
results on high-risk and at-risk students enrolled in an introductory
engineering course. Only half chose to participate in SI, but they earned higher
grades than their counterparts.
Educators have investigated factors that
influence student attendance in academic support programs. Based on student
surveys and interviews, Hodges (1997) reported that students attributed their
non-participation in SI and tutoring to time conflicts and having unrealistic
positive perceptions regarding their own academic abilities and skills. False
feelings of success led students to believe that they did not need additional
Other research on noncognitive factors have been
reported in the literature. For example, student participation may be influenced
by factors such as locus of control, self-efficacy, and self-esteem. In a study
by Visor, Johnson, and Cole (1992), students with an internal locus of control
were likely to participate in SI as were students with the highest self-esteem.
The researchers found that high-risk students--those with an external locus of
control, low self-efficacy and low self-esteem--did participate in SI, but their
attendance was sporadic and they ceased to participate after only a few
Studies on students' motivation and SI participation suggest
that motivation alone does not account for the significant differences in
student outcomes in SI and non-SI groups. Blanc et al. (1983) studied over 700
students in the entry-level courses in four academic disciplines at UMKC. The
students were divided into three groups: (a) SI (i.e., attended one or more
times); (b) Non-SI Motivational Control Group (i.e., on a Likert scale indicated
a high interest in attending but could not because of a work conflict or another
class conflict); and (c) Non-SI Other (i.e., not attending for personal or other
reasons). Differences in the performance data showed that the SI students had
similar college entry data to those in both non-SI groups; their average GPAs
for the semester were significantly higher than both non-SI groups; their
average course grades for the semester were significantly higher than those of
both non-SI groups; fewer D and F grades and fewer Ws were recorded by the SI
group than in both non-SI groups. Blanc et al. found that the differences
between the SI group and the motivational control group were significant in
course grade, in semester GPA, and in percentage of unsuccessful
Still, educators wanted further exploration into why SI
participants academically outperform their fellow students, and they continued
to grapple with the issue of motivation and experimental design. In one study
(Center for Supplemental Instruction, 2000) baseline data were developed before
SI was introduced. Several grade distributions of the same professor for the
same class were studied. Because professors vary in their choice of criteria and
in their grading, a baseline was completed to compare academic performance
before and after SI was created for each professor's class. The introduction of
SI resulted in significant differences in performance outcomes for the SI group.
When the lack of an SI leader removed the SI component from the class, the
performance outcomes returned to the baseline profile suggesting that other
variables in the class did not change. Returning to the baseline also suggests
that students other than those who receive high grades are attracted to the
In another study (Center for Supplemental Instruction, 2000)
researchers developed a quasi-experimental protocol (in conjunction with the
Program Effectiveness Program of the U.S. Department of Education) to help
measure the role played by students' motivation in their success. In Winter
1996, all UMKC students enrolled in courses with SI were surveyed (using a
Likert scale) on the first class day before SI session times were announced to
determine their interest in attending SI. The session times were not announced
until the second class day, so those students were unaware of any time
conflicts. The students were surveyed again on the last class day of the
semester; those who did not attend SI were asked to select from the list of
choices a reason for not participating. Students who selected a time conflict
with another class or work and who on the first survey had shown a high degree
of motivation to attend were designated as the Non-SI Motivational control
group. The resultant three groupings (SI, Non-SI control group, and Non-SI)
showed significant differences. The SI group had higher average course grades
and fewer Ds, Fs or Ws than both Non-SI groups. Significant differences in
course grade and in the percent of unsuccessful enrollments were shown between
the SI group and the control group, which could not solely be accounted for by
Kenney (1988) used a "double exposure" to course content, a
related issue to motivation, to see if this might be the most significant
variable. Kenney conducted the study at the University of Texas at Austin where
students were assigned to one of two groups with mandatory attendance: a
traditional discussion group and a discussion group incorporating SI methods.
The group using SI methods emerged with higher performance.
Based on the
previously reviewed studies, the authors found minimal research on the effect of
mandating students into academic support programs, particularly low achieving
students. Furthermore, the current UMKC SI model does not endorse mandating
students into SI programs. This study challenges the premise that for SI to be
an effective academic intervention, students must participate
The study was conducted at a large state
university in the southern United States enrolling approximately 21,000 students
during the fall, 1994 semester. Freshman students were admitted to the
university based on two performance measures: high school rank and standardized
test scores on the Scholastic Aptitude Test (SAT) or American College Test
(ACT). Freshman applicants who were in the top three quarters of their classes,
and whose high school rank and test scores placed them near the general
admission requirements, were eligible for an individual review. Students whose
academic record demonstrated potential for academic success at the institution
were offered admission. Approximately one-third of the freshman class entered
the institution under individual review.
Subjects consisted of 432
students who self-enrolled in four sections of U.S. History, a high-risk,
required, freshman-level, writing-intensive course. The four sections were
taught by different instructors and all used a standard course syllabus with the
same objectives and expected outcomes. In three class sections, SI was conducted
using UMKC's SI model of 1-hour sessions held several times each week outside of
class for interested students. However, in one class section, SI was integrated
into the class curriculum. The instructor lectured twice each week for 50
minutes (on Monday and Wednesday), and then 10 undergraduate SI leaders
conducted one 50-minute SI session each week (on Friday) in various rooms on
campus during the scheduled class time. The 108 students enrolled in this class
were divided into 10 groups with 10 to 12 students per group.
All of the
SI leaders in this study were undergraduates and attended 3 days of training
using UMKC's SI model. In addition, SI leaders attended regularly scheduled
weekly meetings with the SI director, the course instructor, or both. Each SI
leader was also observed at least three times during the semester by the SI
director or staff to provide feedback and facilitate their growth as an SI
leader. Seventy-nine percent of the students were freshmen. More females (64%)
were represented in the sample than the 54% in the general university
population. Minority participation was 26% and reflected more closely the
institution's minority enrollment. Eighty-five percent of the students were
traditional-age, and 70% were admitted to the university under regular admission
standards, which also mirrors the university's general population. The average
Scholastic Aptitude Test (SAT) composite score of the participants was 893
compared to the university-wide average of 900.
To assess possible
differences in academic motivation among the three groups, the researchers
administered a pre- and post-motivation survey during the first and last weeks
of the semester. The researchers selected the Academic Motivation Scale, a
20-item survey using a 9-point Likert scale, constructed and validated by Baker
and Siryk (1984). The items pertained to academic motivation such as personal
standards regarding academic motivation, academic values and interest, diligence
in meeting past academic obligations, attitudes toward intellectual activity,
self-assessment of aptitude and preparedness for college work, interest in the
particular institution the students would be attending, and future plans
requiring academic effort. In order to accommodate the institution's
computerized scanning format, the researchers reduced the 9-point Likert scale
to four points (strongly agree, agree, disagree, strongly disagree); however,
this did not affect the instrument's reliability. Baker and Siryk obtained a
coefficient alpha reliability of 0.88 on the 9-point scale, and the current
researchers obtained 0.874 on the 4-point scale.
In this study, the
independent variable consisted of the three groups: mandatory SI, voluntary SI,
and non-SI. To be included in the voluntary SI group, students attended at least
one SI session. The two dependent variables were final course grades and
semester GPAs. Using analysis of variance (ANOVA), and when appropriate post hoc
comparisons, the researchers compared mean final course grades in U.S. History
and semester GPAs for the three groups. ANOVAs, chi-square analyses and post hoc
comparisons were also used to test for between-group differences. Data for the
study were analyzed using the CRUNCH (Crunch Software Corporation, 1991)
statistical processing program.
This study has the
limitations of many studies conducted in the naturalistic setting of a
university environment when investigating a particular academic support
program's effect on students' academic success. The study was conducted at a
single institution, whereby it may be difficult to generalize the results to
other institutions. The participants were not randomly assigned into groups;
students self-selected their history sections. In addition, other academic
support programs were available to all participants (the learning center, the
writing center, tutoring, etc.).
Some of the variability may also be due
to differing instruction by faculty members. In particular, the instructor
mandating students into SI had to condense her 3 hours of lecture into 2 hours
each week. These students were given additional readings not covered in class,
and SI leaders facilitated students' discussions over these readings, thereby
giving these SI leaders an additional responsibility not given to the other
self-selected into the U.S. History sections, statistical analyses were
conducted to determine initial differences among the groups. Males were
underrepresented in all three groups: 32% were in the mandatory group, 25% were
in the voluntary group, and 43% in the non-SI group. A chi-square analysis found
a significant relationship (p = 0.0042) between the groups and gender; the
pattern of percentages seem to indicate that fewer males chose to voluntarily
attend SI, which was unexpected by the researchers. Minority student
representation for the sample was 26%. Using chi-square analysis of groups by
ethnicity, no significant relationship was found. Most participants were
traditional age and the mean ages were: 19.1 for the mandatory group, 18.3 for
the voluntary group, and 19.8 for the non-SI group. Results of a one-way ANOVA
indicated significant differences between groups. A post hoc comparison
indicated that students in the voluntary group were slightly younger than the
other groups (p = 0.0103). As mentioned previously, approximately one-third of
each freshman class entered the institution under individual review, and the
participants in this study reflected this admission practice. The majority of
students were admitted under regular university admissions standards: 61% for
the mandatory group, 68% for the voluntary group, and 65% for the non-SI group.
No significant relationship was found between groups' admission status using a
Because SI targets high-risk courses rather than
high-risk students, the researchers' expectations of similar SAT composite
scores among the groups were confirmed. The mean scores were 895 for the
mandatory group, 871 for the voluntary group, and 904 for the non-SI group; a
one-way ANOVA found no significant difference. However, the same expectation of
similarity in high-school rank, a secondary measure of academic preparedness
used by the institution to determine admission eligibility, was not confirmed. A
one-way ANOVA of mean high school rank resulted in significant differences (F=
3.63, df 2, 392, p= 0.0274). Post hoc (i.e., Bonferroni) comparisons revealed
that students' high school rank in the voluntary group, with a mean rank of
72.88, was significant (p=0.0301) over students in the mandatory SI group
(67.36), and the non-SI group (69.10).
Common concerns about higher motivation levels of participants
in traditional SI programs prompted the researchers to measure the academic
motivation of all students before and after conducting the SI intervention. A
comparison of initial motivation levels of the three groups using a one-way
ANOVA found significant differences. Post hoc comparisons revealed that
motivation scores were significantly higher for the SI voluntary group when
compared to the mandatory SI and non-SI groups (see Table 1).
follow-up measurement of motivation at the end of the semester, and subsequent
comparison of mean scores with another one-way ANOVA and post hoc comparisons,
revealed that students in the voluntary SI group maintained their higher
motivation level over students in the mandatory SI group throughout the study.
However, motivation scores for students in the non-SI group was no longer
significantly different from the voluntary group. Fewer students took the
post-test in the non-SI group which may have influenced the outcome (see Table
Final Course Grades
In order to test for significance between
all three groups, grades were converted into numeric values using a traditional
4-point scale (A = 4 points, B = 3, C = 2, D = 1, F = 0, and W = missing data).
A mean was calculated for each group based on the numeric value assigned to each
student's grade. The mandatory group had a mean of 2.74, the voluntary group had
a mean of 2.49, and the non-SI group had a mean of 2.13. A one-way ANOVA for
course grades found significant differences (F= 13.30, df 2,383, p = 0.0000).
Post hoc (i.e., Bonferroni) comparisons revealed that grades were higher for the
mandated group when compared to the non-SI group (p = 0.0000); and the voluntary
group's grades were higher than the non-SI group (p= 0.0136).
of ABC versus DFW history grades for students differed considerably. Students in
the mandatory SI group obtained the highest percentage (91%) of As, Bs, and Cs,
followed by students in the voluntary SI group (81%) and the non-SI group (59%).
The corresponding DFW rates for the three groups were 9%, 19%, and 41%,
Semester GPA by Group
Semester GPA means for
students in the three groups were as follows: mandatory group was 2.70,
voluntary group was 2.70, and non-SI group was 2.36. Because course grades
contribute to GPA, the expectation that mandatory SI participants would earn
higher GPAs than non-participants was supported by a one-way ANOVA result (F=
11.16 df 2, 425, p = 0.0000) and post hoc (Bonferroni) comparisons (p = 0.0004).
In addition, GPA significance occurred for students in the voluntary group
compared to the non-SI group (p = 0.0005), but there were no differences between
GPAs earned by students in the mandatory and voluntary
One major result of this study confirmed
previous SI research findings; students who participated in SI earned higher
course grades and semester GPAs than students who chose not to participate. As
expected by the researchers, motivation was higher for students who participated
voluntarily in SI. Educators have long argued that students who participate
voluntarily in academic support programs such as SI are likely to be more
motivated for college, and because they are more motivated, they are more
The second and most intriguing finding was that
students mandated into SI were less motivated, but performed as well
academically as students who participated voluntarily. It seems logical that
students forced to do something might rebel, and SI leaders indicated that many
students were not overly enthusiastic about attending mandatory SI sessions once
every week. Attendance was mandatory as stipulated by the instructor; SI
absences would lower students' grades. One possible explanation for the success
rate of the mandatory group was their regular weekly attendance in SI; they were
required to attend 13 SI sessions throughout the semester. The researchers did
not conduct a correlation analysis on SI attendance rates between groups;
however, few students in the voluntary group attended more than 10 SI sessions.
Additionally, the researchers did not track the number of times students
attended more than one SI session per week (students voluntarily attending SI
could attend up to three sessions per week; students mandated into SI could
attend only one SI session per week).
Establishing mandatory SI did have
several drawbacks. The researchers were concerned if students in the mandatory
SI freshman history section, attending 2 hours of class instruction, were
learning the same amount of material as those in the other sections (receiving 3
hours of instruction). The instructor teaching the mandatory section had to
restructure and condense her lectures to fit into 2 hours of instructional time
each week instead of 3 hours. Students also had additional readings that were
not covered in class, and SI leaders facilitated discussions on these
Another drawback was that mandatory SI in this study was not
cost effective for the campus learning center. The 10 SI leaders, hired for the
mandatory section, conducted one SI session each week, which cost the same as
hiring four traditional SI leaders holding SI sessions three or four times each
week. Luckily, the researchers had funds from an internal institutional grant to
support the program. Finding 10 available rooms during peak class time was also
a difficult task. Campus resources were limited and some of the rooms were less
conducive to facilitate discussion or had to be scheduled in less accessible
areas on campus.
Conclusions and Recommendations
supports previous research that students who voluntarily participate in SI
benefit academically by earning higher grades and semester GPAs than students
who choose not to participate. The study also provides new evidence to the field
that students mandated into SI also benefit by earning significantly higher
course grades in SI-supported courses and higher semester GPAs than
nonparticipants. Another finding was that not all students, particularly males,
perceive the need for academic support.
From these results the
researchers posit that when students are exposed to effective learning
opportunities (i.e., spending time on task, processing and reflecting on the
lecture material, asking questions without fear of the instructor's evaluation,
and implementing appropriate learning strategies), academic success occurs.
Often instructors simply lecture but rarely help students make the connection
between teaching and learning; SI may help students make that
The results also support educators requiring students to
participate in SI as effective academic intervention. However, mandatory SI is
expensive and may require extensive revision of course content to accommodate SI
as part of the course. One recommendation to remedy these two concerns is
offered. Mandatory SI sessions could be a required, non-credit, laboratory
experience for high-risk courses. The laboratory, scheduled once a week, could
assess a small laboratory fee to provide revenue to pay the SI leaders. Course
instructors would still participate in mentoring the SI leaders, but no change
in the structure of the course would be needed. Another recommendation, based on
prior success at UMKC, is to schedule one SI session weekly that fits the
schedule for students who have been assessed as academically underprepared.
Academic advisors would not schedule other classes at this time for these
Additional research is needed to replicate the findings of this
study on the mandatory, voluntary and non-SI participation of students. Another
area of interest is to investigate if men perceive less need for academic
support than women.
Mandating students into academic support programs
does seem to return to a more in loco parentis environment for postsecondary
institutions. However, to meet the needs of college students in the 21st
century, educators might want to look to their past to seek new solutions for
their future. Requiring students to attend academic support programs, such as
SI, may be one of those solutions.
Allen, M., Kolpas,
S., & Stathis, P. (1992, October). Supplemental Instruction in calculus at
at community college. Colaborative Learning Exchange Newsletter,
Anker, E. O. (1991). Supplemental Instruction: An answer for the
at-risk student in a high-risk course? Unpublished master's thesis, Calvin
College, Grand Rapids, MI.
Arendale, D. R. (1994). Understanding the
Supplemental Instruction model. In D. C. Martin & D. R. Arendale (Eds.), New
directions for teaching and learning: vol. 60. Supplemental Instruction:
Increasing achievement and retention (pp. 11- 21). San Francisco:
Baker, R., & Siryk, B. (1984). Measuring academic
motivation of matriculating college freshmen. Journal of College Student
Personnel, (25), 459-464.
Blanc, R. A., DeBuhr, L. E., & Martin, D.
C. (1983). Breaking the attrition cycle: The effect of Supplemental Instruction
on undergraduate performance and attrition. Journal of Higher Education, 54,
Center for Supplemental Instruction. (2000). Supplemental
Instruction: Review of research concerning the effectiveness of SI from the
Missouri-Kansas City and other institutions from across the
United States. Unpublished manuscript, University of Missouri-Kansas
Crunch Software Corporation. (1991). Crunch. [Crunch program].
Oakland, CA: Crunch Software Corporation.
Freidlander, J. (1980). Are
college support programs and services reaching high-risk students? Journal of
College Student Personnel, 21, 23-28.
Hodges, R. B. (1997). The effect of
self-monitoring strategies and verbal prompts on high-risk students' attendance
in tutoring and Supplemental Instruction and their academic achievement
(Doctoral dissertation, Grambling State University, 1997). Dissertation
Abstracts International, 59(02), 0429A.
Karabenick, S. A., & Knapp,
J. P. (1988). Help seeking and the need for academic assistance. Journal of
Educational Psychology, 80, 406-408.
Kenney, P. A. (1988). Effects of
Supplemental Instruction (SI) on student performance in a college-level
mathematics course. Dissertation Abstracts International, 50(02), 378A.
(University Microfilms No. 8909688)
Kochenour, E. O., Jolley, D. S.,
Kaup, J. G., Patrick, D. L., Roach, K. D., & Wenzler, L. A. (1997).
Supplemental Instruction: An effective component of student affairs programming.
Journal of College Student Development, 38, 577-586.
Reittinger, D. L.,
& Palmer, T. M. (1996). Lessons learned from using Supplemental Instruction:
Adapting instructional models for practical applications. Research and Teaching
in Developmental Education, 13(1), 57-68.
Romoser, M. A., Rich, C. E.,
Williford, A. M., & Kousaleous, S. I. (1997). Supplemental Instruction at
Ohio University: Improving student performance. In P. L. Dwinell & J. L.
Higbee (Eds.), Developmental education: Enhancing student retention (pp. 37-44).
Carol Stream, IL: National Association for Developmental
Rosen, S. (1983). Perceived inadequacy and help-seeking. In B.
M. DePaulo, A. Nadler & J. D. Fisher (Series Eds.), New directions in
helping: no. 2. Help-seeking (pp. 73-107). New York: Academic
Visor, J. N., Johnson. J., & Cole, L. N. (1992). The
relationship of Supplemental Instruction to affect. Journal of Developmental
Education, 16(2), 12-18.
Wagner, L. (1982). Peer teaching: Historical
perspectives. Westport, CT: Greenwood Press.
Webster, T., & Dee, K.
C. (in press). Supplemental Instruction benefits students in an introductory
engineering course. Journal of Engineering Education.
Widmar, G. E.
(1994). Supplemental Instruction: From small beginnings to a national program.
In D. C. Martin & D. R. Arendale (Eds.), New directions for teaching and
learning: vol. 60. Supplemental Instruction: Increasing achievement and
retention (pp. 3-10). San Francisco: Jossey-Bass.
Russ Hodges is an
Assistant Professor in the Department of Educational Administration and
Psychological Services at Southwest Texas State University (SWT); Carol Dochen
is Program Director for the Student Learning Assistance Center at SWT; Donna Joy
is the Instructional Programs Coordinator for the Student Learning Assistance
Center at SWT.
Pre-Motivation Survey (N = 422)
Group M SD
Mandatory SI 53.22(*) 7.89
n = 108
Voluntary SI 56.07 7.23
n = 100
Non-SI 52.45(**) 7.44
n = 214
Note. ANOVA (F = 7.91, df 2, 419, p = 0.0004); Bonferroni Post Hoc
((*) p = 0.0443, (**) p = 0.0002)
Post-Motivation Survey (N = 314)
Group M SD
Mandatory SI 52.64(*) 8.63
n = 94
Voluntary 55.63 7.96
n = 84
Non-SI 53.77 7.62
n = 136
Note. ANOVA: (F= 3.13, df2, 311, p = 0.0450); Bonferroni PostHoc:
((*) p = 0.0406)