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variable. The dependent variable in this study is reading comprehension of the Tarbiyah students. The third variable is a kind of variable that will be given
different name based on the point of view. The term schemata, as the third variable, can be translated into such kinds of variable. Schemata are considered as
moderator variable. Moderator variable is defined by Tuckman 1988: 82 as the factor which is measured, manipulated, or selected by the experimenter to
discover whether it modifies the relationship of the independent variable to an observed phenomenon. This variable is also assumed as secondary independent
variable that is selected to determine if it affects the relationship between the primary independent variable and dependent variable. In this research, the writer
is interested to study the effect of independent variable
X
, or teaching methods, on dependent variable
Y
, or reading comprehension mastery of Tarbiyah students, but suspects that the nature of the relationship between
X
and
Y
is altered by the level of a third factor Z, or the student’s schemata, then
Z
can be analyzed as a moderator variable.
C. Population, Sample, and Sampling
1. Population
According to Fraenkel and Wallen 1993: 68 population is the group of interest to the researcher, the group to whom the researcher would like to
generalize the results of the study. The population of this research is the students of English 3 class of Tarbiyah Department of STAIN Pekalongan in 20112012
academic years. It consists of 4 classes 150 students.
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2. Sample
A sample is a set of elements taken from a larger population according to certain rules Christensen 2000: 158. The sample used in the research is two
classes: 1 38 students of A class, and 2 38 students of B class. Class A is the experimental class and class B is the control class.
3. Sampling
The writer uses cluster random sampling to get the sample. Cluster random sampling is the selection of groups, or clusters, of subjects rather than individuals
Freankel and Wallen, 1999: 72. The step of the sampling are: 1 from the 4 homogeneous classes, two classes are taken randomly; the classes which are
chosen are class A and class B; 2 from those two classes, the researcher chose the class randomly, one as an experimental class and the other as a control class.
Arikunto 2006:133 suggests that cluster random sampling can be used if the number of the population is too large to be observed wholly. Considering the
number of population the technique of cluster random sampling is used to take the samples. Each class is divided into two groups, students who have high level of
schemata and the students who have low level of schemata. One of the classes is taught by Group Investigation Method and the other is taught by the Direct
Instructional Method. So, there are four groups: 1 students with high level of schemata who are taught by Group Investigation Method; 2 students with high
level of schemata who are taught by Direct Instructional Method; 3 students with low level of schemata who are taught by Group Investigation Method; and
4 students with low level of schemata who are taught by Direct Instructional Method.
D. Technique of Collecting the Data
