Instrumentation
In this research, Nelson test was administered as proficiency test to find out the homogeneity of the two groups. The teacher made test was administered in order to determine the participants’ level of proficiency in these groups, so that to make sure there is no significant difference between these two initial groups. The vocabulary items used in the study are selected from an initial list of 99 words. This word list is in the form of sets of words. Pre-test was given before the treatment. The same test was repeated as a post-test after the treatment.
Nelson English Language Proficiency Tests
This test was administered to all the initial participants as a standard
measurement to determine their level of proficiency in both groups in order to make sure that the first two groups are homogenous. The test was selected from the book Intermediate Nelson English Language Tests.
Procedure
In order to conduct the research and verify the research hypothesis, the following steps were taken: first, two groups of 59 and 69 participants of Pardazesh Institute were selected; then a Nelson test was given to find the homogeneity of the both groups. After doing data analysis, the participants whose scores fell one standard deviation above or below the mean were selected. The rest of the 50 participants, were discarded from the study. Finally, the researcher chose 78 participants based on simple random sampling. After random sampling the researcher divided these samples into three different classes; one as semantically related sets, the other as semantically unrelated sets, and finally, the last one as thematically related sets which each of them includes 26 participants. In order to teach vocabularies; the teacher can give synonyms and antonyms, use exemplifications, dramatizations (demonstration), explanations, definitions, and L1 equivalents. The teacher may use these techniques base upon the kind of the words which he wants to teach. After that they are given a few minutes to skim the text, and they discuss the main ideas. Next students read the text again and high light the new words in the text.
Design
In the present study more than one dependant variables were used and there is no randomization therefore quasi-experimental design was applied as the research design. Quasi-experimental designs are practical compromises between true experimentation and the nature of human language behavior which we wish to investigate. By using a quasi- experimental design, we control as many variables as we can and hedge the power of our generalization statements. The sampling design in this study is intact group design as there was no chance for randomization. These elements are found in quasi-experimental designs, such as not grouping by randomization, pre- and post testing and treatment (Hatch & Farhady, 2007). There were three groups in the present study and each group has only one independent variable.
The schematic representation of the research design can be illustrated as follows:
Table 3.1: The research design

Groups

Pre-test

Treatment

Post-test

۱-semantically related

T1

X1

T1

۲-semantically unrelated

T1

X2

T1

۳-thematically related

T1

X3

T1

Data collecting procedure
The statistical analyses, which were used to answer the research question of the study, are listed as below:
A simple and famous formula for comparing means.
Computing the variances of all scores to see homogeneity of three groups.
Computing ANOVA to test the significance difference among means of three classes on the vocabulary learning post-test.
Computing Multiple Liner Regression.
Data Collected
At last, the researcher collected all scores to analyze. All scores which obtained during the following procedures (proficiency test, pre test and post test), were represented in Appendix. Chapter four represents data analysis and the results of each test in every group.
Chapter four