Key facts & rules

• Mean uses all values — affected by outliers.
• Median is the middle value when ordered — not affected by outliers.
• Mode is the most frequent value.
• For grouped data: use midpoints to estimate the mean.
• Cumulative frequency graph: S-shaped curve; read median and quartiles from it.
• Box-and-whisker plots: show median, Q1, Q3, min and max.
• Positive correlation: both variables increase together. Negative: one increases as other decreases.
• The line of best fit passes through the mean point (x̄, ȳ).