Everett Lee proposed a comprehensive theory of migration in 1966. He begins his formulations with certain factors, which lead to spatial mobility of population in any area.
These factors are:
(i) Factors associated with the place of origin,
(ii) Factors associated with the place of destination,
(iii) Intervening obstacles, and
(iv) Personal factors.
According to Lee, each place possesses a set of positive and negative factors. While positive factors are the circumstances that act to hold people within it, or attract people from other areas, negative factors tend to repel them (Lee, 1975:191). In addition to these, there are factors, which remain neutral, and to which people are essentially indifferent. While some of these factors affect most of the people in the area, others tend to have differential effects. Migration in any area is the net result of the interplay between these factors.
Lee suggests that individuals involved in migration have near perfect assessment of factors in the place of origin due to their long association. However, the same is not necessarily true for that of the area of destination. There is always some element of ignorance and uncertainty with regard to reception of migrants in the new area (Lee, 1975:192).
Another important point is that the perceived difference between the areas of origin and destination is related to the stage of the lifecycle of an individual. A long association of an individual with a place may result in an over-evaluation of positive factors and under-evaluation of negative factors in the area of origin. At the same time, the perceived difficulties may lead to an inaccurate evaluation of positive and negative factors in the area of destination.
The final decision to move does not depend merely upon the balance of positive and negative factors at the places of origin and destination. The balance in favour of the move must be enough to overcome the natural inertia and intervening obstacles. Distance separating the places of origin and destination has been more frequently referred to in this context by authors, but according to Lee, distance while omnipresent, is by no means the most important factor (Lee, 1975:193). Furthermore, the effect of these intervening obstacles varies from individual to individual.
Apart from the factors associated with places of origin and destination, and the intervening obstacles, there are many personal factors, which promote or retard migration in any area. Some of these are more or less constant throughout the life span of an individual, while others tend to vary in effect with the stages in life cycle. It may be noted that the real situation prevailing at the places of origin and destination are not as important in affecting migration as individual’s perception of these factors. The process of perception depends, to a large extent, on the personal factors like awareness, intelligence, contacts and the cultural milieu of the individual.
The decision to migrate is the net result of the interplay among all these factors. Lee pointed out that the decision to migrate is, however, never completely rational. Also important to note here is the fact that not all persons who migrate do so on their own decision. Children and wives move with the family where their decisions are not necessarily involved. After outlining the factors at origin and destination, and the intervening obstacles and personal factors, Lee moves on to formulate a set of hypotheses concerning the volume of migration, streams and counter-streams, and the characteristics of migrants.
With regard to the volume of migration, Lee proposed the following set of hypotheses:
1. The volume of migration within a given territory varies with the degree of diversity of the areas included in that territory.
2. The volume of migration varies with the diversity of the people in that territory.
3. The volume of migration is related to the difficulty of surmounting the intervening obstacles. In other words, the more is the intervening obstacles the less is the volume of migration.
4. The volume of migration varies with the fluctuation in the economy.
5. Unless severe checks are imposed, both volume and rate of migration tend to increase over time.
6. The rate and volume of migration vary with the state of progress in a county or area.
Likewise, with respect to the development of streams and counter-streams of migration, Lee suggested the following six hypotheses:
1. Migration tends to take place largely within well defined streams.
2. For every major migration stream a counter stream develops,
3. The efficiency of a stream (measured in terms of a ratio between stream and counter-stream, or the net redistribution of population effected by opposite flows) is high if negative factors at the place of origin were more prominent in the development of stream.
4. The efficiency of a stream and counter stream tends to be low if the origin and destination are similar.
5. The efficiency of migration stream will be high if the intervening obstacles are great.
6. The efficiency of migration stream varies with the economic conditions. In other words, it is high in the time of prosperity and vice versa.
And finally, Lee outlined the following hypotheses relating to the characteristics of the migrants:
1. Migration is selective in nature. Due to differences in personal factors, the conditions at the places of origin and destination, and intervening obstacles are responded differently by different individuals. The selectivity could be both positive and negative. It is positive when there is selection of migrants of high quality, and negative when the selection is of low quality.
2. Migrants responding to positive factors at destination tend to be positively selected.
3. Migrants responding to negative factors at origin tend to be negatively selected.
4. Taking all migrants together, selection tends to be bimodal.
5. Degree of positive selection increases with the difficulty of intervening obstacles.
6. The heightened propensity to migrate at certain stages of life cycle is important in the selection of migration.
7. The characteristics of migrants tend to be intermediate between the characteristics of populations at the places of origin and the place of destination.
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