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
Table 4.2 Descriptive Statistics of Writing Ability Data
of Rater 1 and Rater 2
Rater 1 Rater 2
Mode 73.00
74.00 Median
73.50 67.00
Mean 74.77
67.02 Minimum
58.00 42.00
Maximum 90.00
87.00 Range
32.00 45.00
Semi-interquartile Range 6.75
13.75 Standard Deviation
6.46 9.43
Variance Coefficient 8.64
14.07 Skewness
0.56 -0.32
Standard Error of Skewness 0.31
0.31 Skewness Ratio
1.81 -1.03
Kurtosis 0.48
-0.02 Standard Error of Kurtosis
0.61 0.61
Kurtosis Ratio 0.79
-0.03 Based on Table 4.2 represented above, in terms of the central tendency of
data distribution between the two raters, the most frequently scores of the first and the second rater found respectively are 73.00 and 74.00. Next, it is found that the
median and mean scores of the first rater is higher than the second rater Median=73.5067.00 and Mean=74.7767.02. Similarly, the higher scores are
also found in the first rater in the case of the minimum and maximum scores in comparison to the minimum and maximum scores of the second rater
Minimum=58.0042.00 and Maximum=90.0087.00. In addition, according to Table 4.2, the variability of data distribution
between the first and second raters also encounters some various scores. First, the first rater is found to have the lower range score than the second rater
32.0045.00. Meanwhile, it is found that the semi-interquartile obtained from the first rater is lower than the second rater 6.7513.75. Also, the standard
deviation and variance coefficient of the first rater is found to have the lower score than the second rater Standard Deviation=6.469.43 and Variance
Coefficient=8.64 14.07, which mean that the writing ability data set of the first rater is more homogenous than the second rater. Besides, the data distribution
