SIZE
As said earlier, the term "size" refers to what is the total number of people inhabiting an area is. The area may be the world as a whole, a nation, a region, a locality or a ward within the locality, or a household. The number includes both males and females and all age-groups.
GROWTH RATE AND DOUBLING TIME
Growth rate shows the percentage change in population of an area, and is expressed on per year basis. It is computed from quinquennial and decennial censuses of population. Suppose the population of a country is 100-345 in the year 1991 and it has risen to 120,619 in year 2001. Then the decadal growth rate of the population is
((120,619-100,345)/100,345)*100
i.e., 20.20 percent. On a per year basis it may be defined as 2.02 percent per year (average annual rate of growth).
In advanced technical discussions in place of simple growth rate exponential growth rate is preferred. This is computed by using the following formula:
where Pt refers to the population at time t, P0 to the population at time 0, r to the rate of growth and t to the time. For a short time span, it does not matter much whether you use the decadal growth rate method or exponential growth rate method. The former assumes a discrete change in the population size, the latter a continuous change.
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