The population is divided in three age groups :
(a) Young (0-14 years) Pre -redroductive age group.
(b) Adult (15-59 years) Reproductive age group.
© Old ( 60 years and above) Post - reproductive age group .
The distribution of these groups determine the trend of population .
(a) Growing population : Population having larger numbr of individuals of the pre-reproductive age groups show a very rapid rate.
(b) Steady Population : When the pre-reproductive and post- reproductive age group is same then the population remains steady.
(C) Decline Population : Larger number of post- reproductive age groups make population decline.