This is a basic linguistic fact about Dutch grammar (Verb-Second word order in main clauses), which does not require empirical citation.
The claim asserts that a specific Dutch sentence follows V2 word order. This is a basic, uncontroversial grammatical fact about standard Dutch main clauses (where the finite verb occupies the second position, with 'Waarschijnlijk' as the first constituent and the finite verb 'ga' as the second). Basic grammatical rules of standard languages are common knowledge among linguists and native speakers and do not require empirical research papers to verify.