Connecting the Dots

Summarise data with the mean, median and range, show it on dot plots, spot outliers, and compare two groups.

Key ideas

• The mean shares the total equally: add all the values and divide by how many there are.
• The median is the middle value after sorting; for an even count, take the mean of the two middle values.
• The range (largest − smallest) shows how spread out the data is.
• An outlier is a value far from the rest; it changes the mean much more than the median.
• A dot plot puts one dot for each value above a number line, showing clusters and gaps.
• If the mean and the count are known, the total is mean × count, so a missing value can be found.

Remember

Watch out

• Finding the median before putting the values in order.
• Forgetting a zero value when counting how many values there are.
• Giving the largest value as the range.

Worked example