Points to keep in mind when analyzing trends in population size/growth, total fertility rates and life expectancy

1. It is important to focus on % change rather than the change in absolute numbers when attempting to identify periods of more rapid or less rapid change.   For example, assume a country’s population went from 50 million in 1960 to 170 million in the year 2000.   Also assume that its population increase was exactly 15 million during each 5 year time period.  If you focus on the absolute number of the 5-year change in population – 15 million – you arrive at an assessment that the rate of population change has been constant over time.  If you calculate a 5-year rate of change, though, your assessment would be that the rate of population growth has declined substantially over time: from 30% in 1960-1965 (15 million/50 million *100) from 1960-1965  to 9.7% from 1995 to 2000 (15 million/155 million * 100).  The rate of change method is the more accurate assessment.  If you want to easily calculate an annual rate of change (the standard measure of population change) you can use this Excel spreadsheet:  Calculate and Graph the Annual Rates of Population Growth
   
   
2. It is important to understand the relationship between the Total Fertility Rate and population growth.  There are two points to keep in mind.  First, if the average woman in a country is having 6 children, she will be producing a next generation that is potentially 3 times as large as the current one.  She has “replaced” herself and her mate (1 couple, 2 people) with 6 people (3 future couples).  So long as the TFR is somewhat above 2, the fertility level is above its “replacement level” and the population is likely to increase.  Second, even after the TFR falls below replacement, say to 1.9 which is just a bit below replacement, the population is likely to increase for a while since the % of women in their reproductive years will remain artificially high for several generations in societies that are moving from larger family sizes to smaller family sizes.  After thirty years or so with a below replacement TFR, population size will begin to decrease as the overall structure of the population ages and smaller cohorts of women have entered their reproductive years and are producing future generations that are smaller than themselves.
   
   
3. The shape of these bar charts in the IF program can be a bit deceiving since the the y-axis never is really set at “0", but always at the lowest value contained in the chart.  This kind of charting does allow you to “see” even small changes, but it can be misleading about their true significance.