Costs and Risks of Long Distance Migration
Throughout most of recorded human history, costs have been an obvious operative constraint limiting long distance migration. The expense of gathering information about opportunities elsewhere, and of overcoming distance and other barriers to movement, has been high relative to the potential benefits of relocation. Partly for these reasons, most people most of the time have preferred to stay put or move only within locally familiar regions. During the early 1900s, however, more powerful limits on transatlantic relocation from Europe were imposed not by costs but by fluctuating availability of opportunities in America, and by the perceived net increase in risk associated with pursuing them relative to staying home.
Of course, the costs and risks of migration overlap with each other(and with other factors), and so the risks can be interpreted as a premium on top of more explicit costs of moving. Long distance relocation costs, however, have generally been undertaken as a kind of bet on a likely many-fold payoff in the form of future economic gains derived from working and living abroad. Thus migration costs can also be viewed as a component of the stake put at risk by migration gambles.
Overlap is not the same as equality, however. Usually, migration costs can be roughly gauged in advance. If they are not too high, such costs can usually be over-come with money, time or ingenuity. Migration risks, in contrast, are more uncertain and variable. They can at best be only partially overcome, and are more often managed or endured (or they are avoided by avoiding migration).
Business of Transatlantic Migration, pp. 255-56