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JKM > Volume 43(2); 2022 > Article
Chae, Lee, Han, Cho, and Kim: Study on the Academic Competency Assessment of Herbology Test using Rasch Model



There should be an objective analysis on the academic competency for incorporating Computer-based Test (CBT) in the education of traditional Korean medicine (TKM). However, the Item Response Theory (IRT) for analyzing latent competency has not been introduced for its difficulty in calculation, interpretation and utilization.


The current study analyzed responses of 390 students of 8 years to the herbology test with 14 items by utilizing Rasch model, and the characteristics of test and items were evaluated by using characteristic curve, information curve, difficulty, academic competency, and test score. The academic competency of the students across gender and years were presented with scale characteristic curve, Kernel density map, and Wright map, and examined based on T-test and ANOVA.


The estimated item, test, and ability parameters based on Rasch model provided reliable information on academic competency, and organized insights on students, test and items not available with test score calculated by the summation of item scores. The test showed acceptable validity for analyzing academic competency, but some of items revealed difficulty parameters to be modified with Wright map. The gender difference was not distinctive, however the differences between test years were obvious with Kernel density map.


The current study analyzed the responses in the herbology test for measuring academic competency in the education of TKM using Rasch model, and structured analysis for competency-based Teaching in the e-learning era was suggested. It would provide the foundation for the learning analytics essential for self-directed learning and competency adaptive learning in TKM.

Fig. 1
Characteristic Curve and Information Curve for (A and B) Items and (C) Test.
The solid black line represents Characteristic Curve and the dashed red line the Information Curve of items and test.
Fig. 2
Scale Characteristic Curve for (A) Item 12, (B) Item 13 and (C) Test in Years of 2012, 2016 and 2018 Compared to Those of 2011.
The solid black line is for specific test year of 2012, 2016 and 2018 and the dashed red line for the year 2011 as a reference.
Fig. 3
The Kernel Density Map of Representing Prevalence of Student in Response to Academic Competency in (A) Overall Students, (B) Male and Female Students, and (C) Eight (2011–2018) Years.
Fig. 4
The Wright Map Showing Person Density in Relation to the Item Difficulty in (A) Overall, (B) Male and (C) Female Students.
The red box on the left is for person density and the black marks on the right for item difficulty.
Table 1
Description and Example of Item Response Theory Terms Used in Current Study
Term Description Example in current study
Subject The entity with unique and latent ability or trait to be tested with clinical examination or academic evaluation. 390 students.
Y axis of Figure 3 as a density.
Left side of the Figure 4 as a density.
Ability, Theta (θ) or Competency Unique and latent ability (θ) of a subject rated as a continuous variable with the range of −4 and +4. The academic competency is a major interest of Item Response Theory (IRT) in current study, and it can be used for the absolute evaluation of academic achievement. Table 2 and Figure 2.
X axis of Figure 1, 2 and 3.
 P(θ) and Characteristic Curve P(θ) is a logistic probability function made with item difficulty, discrimination and guessing parameters for estimating latent ability. The Characteristic Curve is an illustrative figure for intuitive understanding of P(θ) in IRT. P(θ) for drawing ICC (Figure 1-A) of item and TCC (Figure 1-C) of test.
 True Score or Expected Value The score representing the latent ability of subject which is estimated using P(θ). Y axis of Figure 1-C.
Y axis of Figure 2.
 Test Score The sum of item scores as for the relative evaluation and Classic Test Theory (CTT). Table 2
Item The basic unit consist of question and answer(s) for competency measure or test score. 14 items used in herbology test
 Item Characteristic Curve (ICC) A curve representing the probability (P(θ)) of getting correct answer corresponding to subject’s ability in specific item. Solid black line of Figure 1-A
 Difficulty (β) It is used for describing how difficulty an item is to achieve 0.5 probability of correct response at a given ability. The difficulty parameter of IRT is negatively correlated with that of CTT. black marks on the right side of Figure 4.
 Discrimination (α) It is the slope of the ICC at the point of 0.5 probability which measures the differential capability of an item. The Rasch model uses 1.0 as for the discrimination parameter. Fixed as 1 in Rasch model
 Item Information Curve (IIC) It shows the amount of information yielded by the item at specific ability level. It can also be used for measuring the reliability of item. Dashed red line of Figure 1-A
Test Collected body of items for analyzing academic competency Herbology test consist of 14 items
 Test Characteristic Curve (TCC) A curve representing estimated test score corresponding to subject’s ability. Solid black line of Figure 1-C
 Test Information Curve (TIC) It shows the amount of information yielded by the test at specific ability level, and it can also be used for measuring the reliability of test. Dashed red line of Figure 1-C
Visualization of test analysis A figure presenting results of IRT analysis for intuitively understanding.
 Scale Characteristic Curve A figure showing estimated score corresponding to specific level of ability. It is useful for comparing estimated score corresponding to specific ability in several groups. Figure 2
 Kernel Density Map A figure showing density of population corresponding to a specific ability. It is useful for intuitive understanding on distribution of subjects across ability levels. Figure 3
 Wright Map or item-person Map A figure with two parts to illustrate whether the difficulty of item is proper for analyzing the ability of subjects; left box is for the distribution of subjects, and right box for difficulty parameter of items Figure 4
Table 2
Test Score and Academic Competency According to Sex and Test Year
Test Score (CTT) Statistics Academic competency (IRT) Statistics
Total (n=390) 10.72±0.11 1.71±0.06

 Male (n=196) 10.61±0.15 T=0.909, p=0.341 1.64±0.08 T=1.424, p=0.233
 Female (n=194) 10.82±0.16 1.78±0.09

 2011 (n=44) 10.2±0.35 F=5.029, p<0.001 (2018>2011, 2012, 2013, 2014, 2016. 2015>2012) 1.46±0.18 F=6.376, p<0.001 (2018>2011, 2012, 2013, 2014. 2015>2012)
 2012 (n=52) 9.98±0.25 1.25±0.11
 2013 (n=47) 10.15±0.3 1.36±0.14
 2014 (n=51) 10.61±0.24 1.57±0.12
 2015 (n=52) 11.29±0.27 1.97±0.15
 2016 (n=47) 10.64±0.35 1.73±0.19
 2017 (n=48) 10.81±0.36 1.81±0.19
 2018 (n=49) 11.98±0.25 2.49±0.17

* Bold represents significant difference found only in the Test Score.


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