Let me defend the position that no one wants: a survey on vacation planning habits cannot directly explain document verification behavior.
It is simplistic to link the act of planning vacations to the diligence of verifying one's passport; many administrative constraints operate independently.
In the UK, for example, the need for a visa for non-EU destinations or the simple reminder of passport renewal via GOV.UK are much more preponderant motivations than just planning a trip.
Correlation is not causality; the information exists, but its explanatory value remains limited without other evidence.