54 Tabel 8. The Result of Validity Instruments
Variable Total of
items Total
Invalid number
items Invalid
item number
Total Valid
number items
Locus of Control X1 30
3 2,3,4
27 Student Perceptions of
Teacher Teaching
Methods X2 30
11 3,5,14
16,20,22 23,25,29
30 19
Parents Concern X3 25
7 11,12,13
14,18,20 24
18
Source. The primary data source has processed. The items fall or not valid have removed and the items are valid
according to researcher is still represented each indicator that wants disclosed, so that the instrument is still eligible to use.
2. Reliability Instrument
The second requirement of a good instrument was to be reliable. The reliability refers to the definition that an instrument was credible
as the data collection tools because since the instrument was good Suharsimi Arikunto, 2010: 221. An instrument was said reliable if it
is used to measure the same phenomenon in different time will show the same results. Testing the reliability of instruments used Alpha
Cronbach formula, as the questionnaire has no answer that is false or zero. The Alpha Cronbach formula used to find the instrument
reliability scores instead of 1 and 0, for example, a questionnaire or subject test. The Alpha Cronbach formula was as follows:
55
r
11
Description: r
11
= instrument reliability k
= the number of the questions ∑α
2
b = the number of variance items
α
2
t = total variance
Suharsimi Arikunto, 2010: 239 Furthermore, the calculations results are interpreted with tables
provide guidelines for the interpretation of the correlation coefficient. Here was the guidelines table:
Table 9. Guidelines for Providing Interpretation with Correlation Coefficient
Interval Coefficient Interpretation
0,00-0,199 Very low
0,20-0,399 Low
0,40-0,599 Enough
0,60-0,799 Strong
0,80-1,000 Very strong
Sugiyono, 2015: 257 The Instrument will be reliable if the coefficient alpha was more
than or equal to 0.600. Conversely, if the reliability is less than 0,600 the instrument is unreliable.
Reliability test results by utilizing the using data processing application programs . The conclusion of instrument Locus of Control,
Student Perceptions of Teacher Teaching Methods and Parents Concern are reliable. Those results can be seen in the following table:
56 Table 10. The Result of Reliability Instruments
No Variable Instruments
Alpha Cronbach
Coefficient Reliability
Description
1 Locus of Control X1
0,615 Strong
2 Students
Perceptions of
Teacher Teaching Methods X2
0,820 Very Strong
3 Parents Concern X3
0,879 Very Strong
Source. The primary data source has processed
I. Data Analysis Techniques
1. Data Description
