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1AM040:JPA2011
The Leading Group Effect: Illusionary
Declines in Scholastic Standard
Scores of Mid-Range Japanese
Junior High School Pupils
Kazuo Mori
Tokyo University of Agriculture and Technology
Purpose
The Z score (“hensachi”) has been considered the
best way to ascertain where a student stands
compared to his or her peers (Saitoh & Newfields,
2010).
However, do the Z scores really reflect the relative
rankings among the groups?
We examined the longitudinal change in the average
Z scores over three years of junior high school pupils.
Method
 Nine cohorts at a junior high school in Nagano
(1998-2009), each consisting of about 200 pupils,
1,962 in total.
 The Z scores from four term exams, the first
mid-term exam in the first year, and the three
year-end exams for 1-3 years.
 Four groups at the quartiles according to the Z
scores on the first mid-term examination: U25,
U50, U75, and U100.
Results
65
60
U100
55
Overall Stability:
The main effect was not
significant for longitudinal
change (F = .97, ns).
U75
50
U50
45
40
U25
35
1st yr 1st yr
1st-mid end
2nd yr
end
3rd yr
end
Fig. 1 Longitudinal change for quartile groups
The mid-range groups
declined:
U100: Gained .74 points
U75: Declined 1.29 points
U50: Declined 1.50 points
U25: Gained 1.84 points
(LSD = .46, p < .05)
Discussion
The distribution was left-skewed
and gradually became less
skewed.
If the distribution is left-skewed
mid-range pupils get
superficially higher scores.
We dubbed this the “Leading
Group Effect.”
Schoolteachers should explain
it to pupils appropriately so they
will not be discouraged by the
illusionary decline.
References
Mori, K. & Uchida, A. (2012). The leading group effect: Illusionary
declines in scholastic standard scores of mid-range Japanese
junior high school pupils. Research in Education, 87 (expected
publication date May 2012).
Saitoh, N. & Newfields, T. (2010). Insights in Language Testing:
An Interview with Shozo Kuwata --A Pioneer of Standardized
Rank Scoring in Japan. SHIKEN: JALT Testing & Evaluation
SIG Newsletter, 14, 2-5.
ACKNOWLEGEMENT
This study is based on Mori and Uchida (2012), a
collaboration with Akitoshi Uchida of Togakushi
Junior High School.

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