Read the passage. A study reported that workers who moved to larger cities earned more than workers who stayed in small towns. Using pre-move salary as the baseline, movers showed substantial gains. Using the salary they had already been offered by local employers, however, the gain was smaller. [Sentence under review] The apparent return to migration depends partly on which realistic alternative is treated as the counterfactual. The authors present both comparisons rather than claiming a single context-free return. What is the most accurate description of the marked sentence’s purpose in the passage’s examination of migration wage baselines?