* State funding models: State appropriations for public universities often significantly subsidize the education of in-state students. Out-of-state students, not contributing to state tax revenue in the same way, aren't eligible for the same level of subsidy. This difference justifies charging them a higher tuition rate to cover a larger portion of the cost of their education.
* Legislature and university governance: State legislatures and university governing boards have the authority to set tuition rates. They typically approve policies that differentiate tuition based on residency status. This isn't a single codified law, but rather a series of state-specific legislative actions and university board decisions.
* Institutional cost allocation: Universities allocate costs, including faculty salaries, facilities maintenance, and administrative expenses, across all students. Charging out-of-state students a higher rate helps offset these costs.
In short, the evidence isn't a single document but rather:
* State statutes and regulations: These documents will vary by state but often include language authorizing or implicitly permitting differential tuition based on residency. You would need to examine the statutes of each individual state to find this.
* University board meeting minutes and policies: Public universities usually have publicly accessible records of board meetings where tuition rates are set and policies explained.
* State budgets: These will often show the differences in state funding allocated to in-state versus out-of-state students.
Therefore, searching for evidence requires looking at individual states' laws, university policies, and budget documents, rather than a single national law.