Historical Growth of Population
Irosin’s population has grown from 8,644 in 1903 to 56,662 in 2015 with a cumulative increase of 48,081 or 556%. In this 112 years period, the average growth rate of the population is 1.68% per year. From the first census in 1903 to 1918, the population grew by 3.39% annually. There was a sharp decline in growth in the period 1918 to 1939 that rebounded back up to 1.79% annually by 1980. From 1980, there was again a decline to 1990 and increasing trend up to 2.23% by 2000. There is a decreasing trend in annual population growth rate from a high of 3.39% in the period 1903 to 1918 to the present 1.72% for 2010 to 2015. Historically, the growth rate of Irosin is lower than the national and provincial growth rate. For 2000 to 2010 period, Irosin’s annual growth rate of 1.29% is lower than the national growth of 1.90%, the regional growth of 1.46%, and the provincial growth rate of 1.31%. (Refer to Table DE-6)
Fertility and Mortality
The simplest and most commonly used index of fertility is the Crude Birth Rate (CBR) which is the number of births divided by population expressed in thousands. In 2016, the CBR of the municipality is 21 or 23 live births per 1,000 of population. The local trend in CBR fluctuates during the last five years but is generally on the range of 20 to 25 and fertility is generally decreasing. Mortality or the occurrence of death is roughly measured by the Crude Death Rate (CDR) which is the number of deaths per 1,000 of population. The 2016 CDR is 6.38 deaths per 1,000 of population. The CDR of Irosin for the past five years ranges from 7.95 to 6.38 and mortality rate is generally decreasing. Irosin’s CBR in 2013 is 22.6 which is lower than the national CBR of 24.4 in the same year. For CDR, the national rate is 6.52 in 2016 which is higher than the local CDR of 6.38. (Refer to Table DE-7)
The average rate of natural increase (RNI) in population, which is the difference between CBR and CDR, is 1.47% for the past five years. Since the population growth rate is higher than the rate of natural increase, the population is not closed and it is assumed that 0.25% of the growth rate is net of in-migration and out-migration.