Statistics
Statistics
Statistics questions require collecting, organising and interpreting data. Know the difference between discrete and continuous data, construct frequency tables, and read bar charts, pie charts, line graphs and scatter diagrams. Calculate mean, median, mode and range, and interpret these measures. For grouped data, use class midpoints to estimate the mean; understand cumulative frequency and simple correlation. A pie chart uses angles proportional to frequencies, with a full circle representing 360 degrees.
Traps include finding the median without arranging the data in order, using the wrong total frequency, and treating a grouped mean as exact rather than an estimate. In a pie chart, calculate one angle as frequency divided by total frequency times 360 degrees. The mode is the most frequent value, not the largest value. Range is a single number: largest minus smallest. Correlation describes a relationship, not proof of cause. When comparing two data sets, comment on a measure of average and a measure of spread.
Worked example: for 4, 7, 9, 10, mean = (4 + 7 + 9 + 10) / 4 = 30 / 4 = 7.5. Arrange for the median: 4, 7, 9, 10. The middle pair is 7 and 9, so median = (7 + 9) / 2 = 8. There is no repeated value, so there is no mode; range = 10 - 4 = 6.
Rule of thumb: always sort data before finding the median and check the total frequency before calculating any average.