Back

Study

Statistical Skills

Statistical skills involve using measures of central tendency (mean, median, mode), measures of spread (range, interquartile range), calculating percentages and percentage change, and understanding how to use these techniques to analyse geographical data. These numerical and statistical skills are assessed across all three papers.

Mode, median and mean are measures of average, and the range is how spread out the values are: MODE = MOST common value MEDIAN = MIDDLE value (when they are in size order) MEAN = TOTAL of items / NUMBER of items RANGE = DIFFERENCE between highest and lowest values

Key Terms

Mode — The most common value in a data set.
Median — The middle value when all values are arranged in size order.
Mean — The total of all items divided by the number of items. Also called the average.
Range — The difference between the highest and lowest values in a data set.

Exam Tips

  • •Always show your working when calculating mean, median, mode, range, percentages or percentage change -- you may get marks for the method even if the final answer is wrong.
  • •For median: put values in order first. If there is an even number of values, the median is halfway between the two middle values.
  • •For percentage change, remember the formula: ((new - old) / old) x 100. A positive answer = increase, negative = decrease.
  • •The interquartile range (IQR) is useful because it ignores extreme values (outliers) that might distort the range.
  • •When comparing data sets, use measures like mean and range to make precise comparisons rather than vague statements.
  • •Be able to identify weaknesses in how statistics are presented -- for example, using the mean when the median would be more appropriate (if there are outliers), or selecting data to support a biased argument.
  • •Make sure you can interpolate (read between data points) and extrapolate (extend trends beyond the data) using lines of best fit on scatter graphs.
  • •In fieldwork questions, justify why you chose a particular statistical technique -- e.g. 'I used the mean to find the average pebble size because it uses all the data values.'