Development of Three Tier Static Electricity Diagnostic Test to Identify Student Conceptions About Static Electricity

The purpose of this research was to develop and validate Three Tier Static Electricity Diagnostic Test (TTSEDT). The development procedure consists of four stages: define, design, develop, and validation. The subjects of this study consist of 2 physics education experts and 120 high school students, in 12th grade. The response of two experts was used to determine the content validity of TTSEDT. Meanwhile, the students' responses were used to determine the items internal consistency, discrimination index, difficulty index, and reliability index. The reliability of TTSDET was determined by KR-20. The results showed that: (1) TTSEDT meet content validity which means that TTSEDT items are really measures the students' conceptions and misconceptions about static electricity; (2) the items internal consistency index is in the interval 0.20-0.47; (3) the items discrimination index is higher than 0.20; (4) the difficulty index of test items is in the interval of 0.25 - 0.75;  (5) the reliability index  of TTSEDT is 0.73 (p<0.05). TTSEDT is a valid, reliable, and effective instrument for identifying students' conceptions of static electricity.

a) How is the content validity of TTSEDT? b) How are the items internal consistency of TTSEDT? c) How are the items discrimination Index of TTSEDT? d) How is the reliability of TTSEDT? e) Is the TTSEDT effective to identify students' conception about static electricity?

Materials and Methods
The development of TTSEDT consists of four stages: Define, Design, and Develop, and Validation (modified from (Thiagarajan: 1974).

Define
This stage defines the TTSEDT needs related to the conception and misconceptions that occur in static electricity. Scientific concepts are identified from the Basic Competencies of High School Curriculum. Meanwhile, various misconceptions on static electricity are identified from the various literature and research results using ordinary multiple choice tests and two-tier multiple-choice tests such as (Maloney, et al.:2001;Bilal & Erol: 2009;Koudelkova & Dvorak: 2014).

Design
This stage begins with the preparation of a test grid to ensure compatibility between test items and the concepts to be measured. The first tier of TTSEDT is designed in multiple-choice form with four alternative choices. The alternative correct answer is a scientific concept, while alternative wrong answers are misconceptions related to certain concepts. The second tier of TTSEDT is designed in multiple-choice form, with alternative answers in the form of reasons for alternative answers in the first tier. An alternative reason for the correct answer in the second tier is the scientific explanation of the concept, while the alternative wrong answer is a non-scientific explanation. The third tier of TTSEDT is designed in the form of a choice of confidence in the answers in the first and second tiers which are avoided by two alternatives, namely sure and not sure.

Develop
Developed the Three-Tier Multiple Choice Test items in accordance with the identified concepts of the high school curriculum, findings with ordinary multiple choice tests and two-tier tests. Some items are developed from an ordinary multiple choice test from (Maloney, et al.: 2001;Bilal & Erol: 2009;Koudelkova & Dvorak: 2014), and partly developed by the author himself.

Validation
The content validity of the TTSEDT is obtained by analyzing whether the test items really measure key concepts and misconceptions of students about static electricity. Content validation was carried out by two physics education experts. These experts are asked to analyze the items that include item statements, alternative choices, answer keys, and distracted. In the first tier, the experts analyze whether the item statement is easy to understand? Is the answer key a scientific concept? Is the distracters are the variety of students' misconceptions about certain concepts. In the second tier, experts are asked to analyze whether the answer key for student reasons is a scientific explanation and whether distracter is a non-scientific explanation of the concepts asked in the first tier. They made some corrections, comments, and suggestion on some of the items that were used to revise the item. At this stage, pilot testing was performed for internal consistency analysis, discrimination index, difficulty index, and test reliability. Pilot testing

Data Analysis
Data analysis was carried out in a descriptive quantitative and qualitative manner. The content validity is expressed qualitatively based on the expert responses. Calculation of internal consistency index, discrimination index, difficulty index, and reliability of the test is assisted by SPSS for Window. Internal consistency index, discrimination index, difficulty index, and reliability were determined from the third tier score. In the third tier score of 1 is given if the student's answer in the first tier is right, the reason in the second tier is right and the third tier answer is "sure". The score of 0 is given for the other answers. Reliability index is calculated by KR-20 formula (Arikunto: 2009). Variety of students 'conceptions are categorized into the scientific concept, lack of confidence, misconception, and lack of knowledge based on a combination of students' answers in the first, second and third tiers with criteria as in Table 1.

Content Validity
According to experts, the TTSEDT developed meet content validity. This means that TTSEDT items are really measuring the students' conceptions and misconceptions about static electricity. In the first tier, the answer keys are scientific concepts and the distracters are the non-scientific concepts. In the second tier, answer keys are the scientific explanations of the concept and the distracters are the nonscientific explanation. In this study, the test material includes concepts of charge, electrostatic force, electric field, potential energy, electrical potential, and capacitors. This material was derived from the 12 th -grade high school curriculum.

Items Internal Validity
Of the 30 items tested, there are 29 items that have an internal validity index in the range of 0.20-0.49 as shown in table 3. These values are greater than the table values (rtable=0.195) at the 5% significance level. This means that TTSDET items are consistent with the entire item.  Table 3 shows a summary of the results of items discrimination index analysis of TTSEDT. There are 21 items (72,4%) which have discrimination index in the medium category, 7 items (24,1%) have discrimination index in the good category, and 1 item ( 3.4%) has a discrimination index in the very good category. Al of the 29 test items have a discrimination higher than 0.20, which means it qualifies as a good test. Discrimination is defined as the ability of a items to distinguish between high-ability students and low-ability students (Arikunto: 2009). That is, if the test is given to students who are clever will be more likely to be answered correctly, whereas if given to learners who have the low ability will be the more wrong answer. There are 21 items (72,4%) which have discrimination index in the medium category, 7 items (24,1%) have discrimination index in the good category, and 1 item ( 3.4%) has a discrimination index in the very good category. Al of the 29 test items has a discrimination higher than 0.20, which means it qualifies as a good test. Discrimination is defined as the ability of items to distinguish between high-ability students and low-ability students (Arikunto: 2009). That is, if the test is given to students who are clever will be more likely to be answered correctly, whereas if given to learners who have the low ability will be the more wrong answer.

Items Difficulty Index
The results of the difficulty index analysis of TTSEDT items are presented in Table 4. The results presented in Table 4 reveal that the TTSEDT items difficulty index is in the medium category. It can be noted in the question bank and can then be used to identify student's conception of static electricity. The difficulty index of all the TTSEDT items is within the range of 0.25 -0.75, so the test can be said well (Kanli: 2015). The level of difficulty serves to determine whether the research instrument used is too difficult or easy for students to measure conceptual knowledge, so the test results can actually show the misconceptions shown by the student. The difficulty level of the item will show how many students as a test participant are able to answer the problem correctly from the given problem.

Reliability Index
By using KR-20 it was found that the TTSEDT reliability index was 0.73. This similar results were obtained by Pesman & Eryilmaz (2010) on the development of the three-tier test for simple electric circuit that is 0.69; Cetin, Dindar, & Geban (2011) that found r = 0.72 for three-tier diagnostic test to assess high school students' understanding of acids and bases; and Oberoi (2017) that found r = 0.79 on three-tier concept achievement test in science. This indicates that TTSEDT is a reliable test for measuring student conceptions. Reliability test is one of the criteria of assessment instruments required other than validity. The test is said to have high reliability if it provides consistent results for repeated measurements. Thus, TTSEDT will give the same results for repeated measurements of students' conception of static electricity.

Students' conceptions of static electricity
TSEDT is effectively used to identify the type of students' conception of static electricity Based on the students' response to each tier, it can be determined the percentage of students whose knowledge is classified into scientific concepts, lucky guess, misconception, and lack of knowledge as presented in table 6.

Conclusion
The developed three-tier static electricity diagnostic test is a valid and reliable instrument to identify 12-grade high school students' conceptions about static electricity. Test items are consistent with the entire item, can distinguish high and low ability students, and have a moderate level of difficulty. By using this three tier static electricity diagnostic test, students' conceptions can be categorized into scientific concepts, lucky guesses, misconception, and lack of knowledge. Three-tier static electricity diagnostic test is easy and quick to assess students' conceptions of electricity. It is suggested to physics teachers to use this test to diagnose students' conceptions of static electricity. The results can provide direction for improvements to be made.

Conflict of interest statement and funding sources
We declare that there is no competing interest in the release of this article. This study was funded by the Directorate Research and Community Service, Ministry of Research, Technology, and Higher Education of the Republic of Indonesia.

Statement of authorship
The authors have responsible for the conception and design of the study. The authors have approved the final article.