coefficient.
2
This design was used to find out the relation between two variables or more and to see the influence of each other. In this case, this design was
employed to seek the relation between critical thinking skill and argumentative writing skill.
C. Population and Sample
The population of this study was twelfth grade students of SMA Kharisma Bangsa, academic year 20152016, included 68 students from 4 Classes. From
the population, 35 students were chosen as the participants of this study. The sample of this study were 35 students that had been selected. The
sample was determined by using purposive sampling technique. Purposive sampling technique means taking sample based on the certain purpose. Two
classes were determined as the partcipants of this study based on the avarage ability both have. In this case, 35 students from XII A and XII C class were
selected and being the subjects of this study. In addition, those students were chosen because they had already learnt argumentative essay.
D. Research Instruments
In this study, there were two instruments to collect the data which were administered to the participants students of SMA Kharisma Bangsa. The
instruments were critical thinking test which attempt to measure students critical thinking skill, and an instruction asking the students to write argumentative essay
which is used to measure students argumentative writing skill. Those instruments were used in order to achieve the goal of the study; to find out the correlation
between those variables. Here, is the specific information of the research instruments:
1. Critical Thinking Test
The critical thinking test used in this research was Cornell Critical Thinking Test series. The CCTT is a standardized test developed by R. Ennis,
Millman, and Tomko in 1980. In this study, level X was chosen as the instrument
2
L. R. Gay, Geoffrey E. Mills and Peter Airasian, Educational Research: Competencies for Analysis and Applications, London: Pearson Education Ltd., 2009, 9
th
ed., p. 196.
to measure the students’ critical thinking skill as the samples of this study were twelfth grade students. This test was considered suitable to be used in the present
study because it is claimed by its developers to be a general critical thinking test which attempts to measure the critical thinking skills as a whole and it is best used
for grade 9 to 12. Level X includes the following skills: induction, deduction, credibility, and identification of assumptions see the instrument in Appendix 1.
Moreover, the test has been widely used throughout the world more than twenty years to measure critical thinking skill. Additionlly, level X was chosen by several
researchers Rosyanti and Rosna Awang: 2008, Rozaidi Ismail: 2003 to measure students critical thinking skills.
The CCTT was already being tested in the term of validity and reliability. The developers argue for the construct validity of the CCTT based on its content
validity. The test was developed based on a sound rationale and that the test items were intensively discussed by the test developers who were scholars involved in
the Illinois Critical Thinking Project. Meanwhile, the developers claimed that the reliability coefficient of the CCTT Level X ranges from .67 to .90.
3
2. Instruction to write Argumentative Essay
This test was conducted to measure the students’ argumentative writing
skill. There were three topics given to develop by the students see the instrument in Appendix 2. The topics were adopted from the students textbook Aim High 6
and Contextual English. In assessing writing, the assessment rubric which was adopted from the
book entitled Assessing Writing was applied in this study. It was developed by Jacob et al, and cited by Sara Cushing Weigle in her book. There were five
categories to be assessed include; content, organization, vocabulary, mechanic and usage see the assessment rubric in appendix 3.
To validate this scoring scheme, two raters were asked to analyze the proposed components, as well as the sub-components. Then, they were required to
3
Ennis, op. cit., p. 3.
