Technique of Data Collection

Table 4.1 Descriptive Statistics of Critical Thinking Ability Data Mode 51.35 Median 51.35 Mean 50.14 Minimum 27.03 Maximum 70.27 Range 43.24 Semi-interquartile Range 13.51 Standard Deviation 8.99 Variance Coefficient 17.82 Skewness -0.11 Standard Error of Skewness 0.31 Skewness Ratio -0.35 Kurtosis -0.09 Standard Error of Kurtosis 0.61 Kurtosis Ratio -0.14 Based on Table 4.1 above, the central tendency distribution of critical thinking ability data of the 60 sixth semester students Department of English Education is indicated by the mode, mean, median, minimum, and maximum scores. In this case, it is found that the most frequently score Mode of critical thinking ability data is 51.35. Next, the middle point in the data distribution Median found is 51.35. Besides, the average score is shown by the Mean score 50.14. Meanwhile, the lowest score Minimum obtained is 27.03, and the highest score Maximum found is 70.27. In addition, the dispersion or variability distribution of critical ability data is shown by the scores of range, semi-interquartile range, standard deviation, variance coefficient, skewness, and kurtosis. First, based on Table 4.1 represented above, the range score between maximum and minimum scores found is 43.24. The next indicator of variability which is based on the range of the middle 50 percent of the test scores is shown by the semi-interquartile range score 13.51. Besides, the standard deviation score found is 8.99. Meanwhile, the percentage of the comparison between standard deviation and the mean scores is shown by the coefficient variance 17.82. Next, the dispersion shape of the data distribution is indicated by skewness and kurtosis scores found respectively are -0.11 and -0.09 both of these scores indicates that the shape of data dispersion is slightly-left skewed and peaked. It is interpreted as a reasonably normal distribution for the skewness ratio -0.35 and kurtosis ratio -0.14 are included in the reasonably accepted score of normal data distribution, i.e. between -2 and 2. Furthermore, to provide an additional vivid description of the data distribution of the critical thinking ability data, Figure 4.2 gives the histogram of frequency distribution with the probability normal curve formed as follows: Figure 4.2 Histogram with Normal Curve of Critical Thinking Ability Data Apparently, Figure 4.2 shows that critical thinking ability data is normally distributed. This is indicated by the histogram which resembles the symmetrical and bell-shaped graphical representation.

2. Writing Ability Data

The writing ability of the sixth semester students of Department of English Education is determined from the students‟ responses in the test of written English independent essay which were rated by two raters. Table 4.2 below describes the comparison scores of the writing ability rated by the first rater and the second rater as follows: Mean: 50.14 Std. Deviation: 8.99