Estimation of an Examinee's Ability in the Web-Based Computerized Adaptive Testing Program IRT-CAT

We developed a program to estimate an examinee s ability in order to provide freely available access to a web-based computerized adaptive testing (CAT) program. We used PHP and Java Script as the program languages, PostgresSQL as the database management system on an Apache web server and Linux as the operating system. A system which allows for user input and searching within inputted items and creates tests was constructed. We performed an ability estimation on each test based on a Rasch model and 2- or 3-parametric logistic models. Our system provides an algorithm for a web-based CAT, replacing previous personal computer-based ones, and makes it possible to estimate an examinee's ability immediately at the end of test.


INTRODUCTION
Although computerized adaptive testing (CAT) has been widely used for large scale examinations and for the assessment of the psychological indices, no freely available, well-documented web-based program is known. An ability estimation algorithm was first described by Baker [1] that can be used for a personal computer base. Kim et al [2] at Busan University in Korea published the java source for a CAT in a textbook first in Korean. However, nowadays the user interface for examination has rapidly changed from personal computer-based to webbased. For a CAT system, the following four components are necessary: -Management system of the examination, including an item bank -System of parametric estimation for the items according to item response theory -System of estimation of examinee's ability -System of reevaluation of items after termination of examination There is no integrated program freely available to execute CAT in the educational fields including the above four categories. Therefore, to provide an open access web-based computerized adaptive testing (CAT) program based on the Rasch model and 2-and 3-parametric logistic models, we tried to make a web-based ability estimation program after constructing the management system of examination, including an item bank.
We developed a program to estimate an examinee s ability in order to provide freely available access to a web-based computerized adaptive testing (CAT) program. We used PHP and Java Script as the program languages, PostgresSQL as the database management system on an Apache web server and Linux as the operating system. A system which allows for user input and searching within inputted items and creates tests was constructed. We performed an ability estimation on each test based on a Rasch model and 2or 3-parametric logistic models. Our system provides an algorithm for a web-based CAT, replacing previous personal computer-based ones, and makes it possible to estimate an examinee's ability immediately at the end of test.

MATERIALS AND METHODS
Tools used for programming were as follows: The key algorithm was already known for the ability estimation [2]. It was coded for web-inferface.

Input of items
Items can be inputted on a website. At first, basic information, such as category, item type, key words, IRT model, item parameters already determined, answer option form and number of answer option (Fig. 1), are added. An item stem can be inputted for text, and flash files can be inputted for multimedia data such as images, sounds and movie (Fig. 2). Items are presented randomly to each examinee. The table structures are shown in Fig. 3.

Search within items
On the screen, key words or text words from the items can be used to search. A Boolean search with two categories is also possible (Fig. 4). As for the CAT, each item that was already analyzed according to the respective IRT model can be searched. Each item's information function is viewed, and the rate of options by examinees in the CAT is also presented (Fig. 5).

Creation of test and the addition of items
To create the test, the title, start and stop time, and type of

Viewing the results of an examination
After the termination of an examination, the results can be shown immediately. The examinee's ability is shown (Fig. 8).
Each examinee's response to each item can be seen after clicking on an examinee's name (Fig. 9). Since the results of the examination were analyzed on the web, there is no need to download result files and analyze them again.

CAT program
Source code of CAT in this paper is freely available at https: (page number not for citation purposes)     The CAT program in this paper has already been implemented in the educational field with easy interpretations of examinees' ability [3].

DISCUSSION
The merits of the present program for the estimation of an examinee's ability are that it is web-based and allows for the immediate estimation of ability after the termination of testing. Also, the selection of the less exposed items was prompt because the results of exposure are recorded in the system. Practical issues in developing and maintaining a CAT program included an item bank, test administration, test security and examinee issues [4]. Out of these, item bank and test administration was also actually addressed in the IRT-CAT program.