Background: Validity is a notable concept in language testing which has concerned many researchers and scholars in the field of language testing due to its importance in decision making process. Tests' results always introduce consequences to test takers' lives which emphasizes the need to ensure their validity. Detecting and delineating the potential sources that may threaten the validity of standardized tests of English proficiency is therefore of great importance. Methods: This study was a quantitative investigation of test validity using an interpretive model. The main purpose of this study was to quantitatively assess and determine the relationship between a series of inferences in an interpretive argument-based framework that can potentially threaten the validity of the test. Results: To this end samples of TOEFL iBT were analyzed and the obtained results determined its validity expressed in terms of the chain of inferences in the interpretive model. Conclusion: The findings indicated that there is a direct relationship between the performance on the TOEFL iBT and the target domain of English language use, observed test scores are reflective of intended academic language abilities, observed test scores can be generalized to similar language tasks in different occasions and test forms, and expected test scores can be accounted for by underlying language abilities in an academic environment.