Everett Lee has conceptualized the factors associated with the decision to migrate and the process of migration into the following four categories: (1) Factors associated with the area of origin; (2) Factors associated with the area of destination; (3) Intervening obstacles; and (4) Personal factors.
Lee elaborates all these four categories by pointing out that, in each area, there are numerous factors which act to drive away the people from the area, or to hold the people in the area or to attract the people to it.
In this respect, there are significant differences between the factors associated with the area of origin and those associated with the area of destination. Migration may take place after both these are properly weighed.
Usually, however, a person has a better and more realistic knowledge about the place of origin, while his knowledge about the place of destination is somewhat superficial and inexact.
Intervening obstacles also have to be overcome before migration finally takes place. These include distance and transportation. Technological advances, however, have lessened their importance in modern times.
Finally, the personal factors are of the utmost importance because, instead of the actual factors associated with the place of origin and/or destination, the individual’s perception of these factors is found to influence the actual act of migration.
Individual differences, too, play their part, as some persons are generally resistant to change of any kind, especially to a change of residence, while others are eager for such a change.
Lee is, therefore, of the opinion that the decision to migrate is never completely rational, and hence it follows that it is always possible to come across exceptions to any type of generalisation about migration.
Another point to take into consideration in this connection is that not all migrants migrate as a result of their own decision; for example, children have generally to go along with their parents, and wives accompany or follow their husbands. Such type of migration is known as sequential migration.
Lee has further attempted to formulate several hypotheses within his conceptual framework regarding the four types of factors associated with migration, which incorporate the push and pull factors both at the place of origin and the place of destination.
These hypotheses cover the volume of migration, the development of streams and counter-streams of migration, the characteristics of the migrants, for explaining why some people migrate and others do not. The hypotheses may be listed as follows:
Volume of Migration:
(1) The volume of migration within a given territory varies with the degree of areas included in that territory; (2) The volume of migration varies with the diversity of the people; (3) The volume of migration is related to the difficulty of surmounting the intervening variables; (4) The volume of migration varies with fluctuations in the economy; (5) Unless severe checks are imposed, both the volume and rate of migration tend to increase with time; (6) The volume and rate of migration vary with the state of progress in a country or area.
Streams and Counter-streams of Migration: (1) Migration tends to take place largely within well-defined streams; (2) For every major migration stream, a counter-stream also develops; (3) The efficiency of the stream (ratio of stream to counter-stream or the net redistribution of population affected by the opposite flow) is high if the major factors in the development of a migration stream are minus factors at origin; (4) The efficiency of the stream and the counter-stream of migration tends to be low if the place of origin and the place of destination are similar; (5) The efficiency of migration streams will be high if the intervening obstacles are great: (6) The deficiency of the migration stream varies with economic conditions, being high in prosperous times and low in times of depression.
Characteristics of Migrants:
(1) Migration is selective; (2) Migrants responding primarily to plus factors at destination term to be positively selected; (3) Migrants responding primarily to min factors at origin tend to be negatively selected; or where the min factors are overwhelming for the entire population group, they not be selection at all for migration; (4) When all migrants are considered together, selection for migration tends to be bimodal; (5) The degree of positive selection increases with the difficulty posed by the intervening obstacles; (6) the heightened propensity to migrate at certain stages of the life-cycle is important in the selection of migrants; (7) The characteristics of migrants tend to be intermediate between the characteristics of the population of the place of origin and of the population of the place of destination.