Population and economic development patterns practice questions.

A student records household incomes in one neighbourhood and finds that most values cluster between US$ 4 000 and US$ 8 000 per year, while three households report more than US$ 90 000. Which measure of central tendency best represents the typical household here?

• The mean, because it uses every value in the data set
• The mode, because it is the value that occurs most often in the data set
• The median, because it is not distorted by extreme values
• The midrange, because it lies halfway between the highest and the lowest value

Answer: The median, because it is not distorted by extreme values

Three very high incomes pull the mean upwards, so it stops describing a typical household, and the midrange is decided entirely by the two extremes. The median is a positional measure and barely moves, whereas incomes recorded to the nearest dollar rarely repeat, so the mode is unstable for ungrouped data of this kind.

On a scatter graph of gross national income per person against life expectancy for 40 countries, one country lies far below the best-fit line. How should a candidate treat that point in an answer?

• Delete the point and then redraw the best-fit line without it
• Treat the point as a recording error made during data collection
• Identify it as an anomaly and suggest a reason for it
• Ignore the point because it does not fit the overall relationship

Answer: Identify it as an anomaly and suggest a reason for it

Anomalies carry marks: naming the country and offering a cause such as conflict, epidemic disease or economic collapse demonstrates analysis, whereas deleting inconvenient data misrepresents the sample.

A world map shades each country according to its gross national income per person. Which limitation matters most to a reader who wants to know where the world's low-income people live?

• Colour classes cannot show more than four categories of data.
• The technique can only be used for absolute totals, not for rates.
• Each country is drawn as a single point, so small states disappear.
• One average is shown for each country, hiding the variation inside it.

Answer: One average is shown for each country, hiding the variation inside it.

Shading a rate is exactly what a choropleth map is for, so the technique is not the problem; the unit is. Large numbers of low-income people live inside middle-income countries, and a national average makes them invisible.

A country records a population density of 25 people km⁻², yet in the same year seven out of ten of its residents live in three coastal cities. Which characteristic of its population does the density figure conceal?

• Population structure
• Population distribution
• Population momentum
• Population projection

Answer: Population distribution

Density is one average of people per unit area; distribution describes where inside that area they actually are. Two countries can share a density figure and look nothing alike, one evenly settled and one clustered on a coast or a river.

A country records a crude birth rate of 28 per 1 000 and a crude death rate of 8 per 1 000 in one year. Calculate its rate of natural increase (to 1 d.p., in %). Answer: ___

Answer: 2.0

Rate of natural increase = (CBR - CDR) / 10 = (28 - 8) / 10 = 2.0 %. Dividing by 10 converts 'per 1 000' into 'per 100', and migration is deliberately excluded from the measure.

A population is growing at 1.4 % per year. Using the rule of 70, calculate its doubling time (to the nearest whole number, in years). Answer: ___

Answer: 50

Doubling time is approximately 70 divided by the annual growth rate in per cent, so 70 / 1.4 = 50 years. The rule assumes the growth rate stays constant, which makes it an estimate rather than a forecast.