Methods of determining distance covered in migration are discussed. "Two approaches for doing so are simply to ask movers how far they moved or to infer distance from localities of origin and destination. The former has been used in Health Interview Surveys, and the latter is applied to Current Population Surveys; both are national surveys conducted by the U.S. Census Bureau. The two approaches appear to produce consistent results and offer ways of increasing comparability of data and research findings on geographical mobility."

Age stands out as an important factor in multiple moves over a relatively short period of time. In addition, in the NHIS data whites show a higher tendency to be multiple movers than do blacks. It was also found that persons defined as interstate migrants moved more often than either intrastate migrants or local movers, but it is impossible to conclude anything more definitive about that relationship. In conclusion, mobility defined as a move rather than as a mover is clearly higher than estimates derived from five-year census data or the CPS, which only use the idea of a mover. On the whole, though, over three-year periods most persons do not move at all or they move and then return. Of those who do change residence, the majority move only once. By far the bulk of moves is accounted for by a relatively small segment of Americans. Of 34,000 moves reported in the NHIS, more than one-half were made by a small number of persons--4,400--who not only constituted scarcely one-fourth of all movers but were less than 1 out of every 11 Americans.