2.5. How quickly are populations growing?
16 This question can be investigated by calculating birth rate minus death rate. Most students realise that this new variable gives some measure of the change in population. Results range from -1.8 (a decreasing population) to 37.8 (an increasing population). The mean is around 18.4, but what does it signify? (Note that these values are "per thousand" so 20 per thousand is 2%.)
17 What happens to a population with an annual growth rate of 2%? How long will it take to double in size? This can be investigated using a spreadsheet, and different growth rates can be compared.
18 Often people do not understand rate of inflation (with regard to prices). This is a rate of inflation with regard to people! What we are looking at is the gradient of the gradient.