Tales by Dots and Lines

Organise data in frequency tables, find the mean, median, mode and range, and read line graphs to compare groups and spot trends.

Key ideas

• A frequency table counts how often each value or group of values occurs.
• In grouped data, a value on the boundary goes in the higher class (10–20 holds 10 but not 20).
• The mean is the total divided by the count; it is pulled by very large or small values.
• The median is the middle value after sorting; with an even count, average the two middle values.
• The mode is the most frequent value; the range (largest − smallest) shows the spread.
• A line graph shows how a quantity changes over time; a steeper line means a faster change.
• Use percentages to compare groups of different sizes.

Remember

Watch out

• Finding the median without sorting the data first.
• Taking the highest frequency as the mode instead of the value that has it.
• Comparing raw counts for groups of different sizes.

Worked example