Food for Thought

Learning Focus

Summarize data with measures of center and spread, and choose measures that fit the data story.

Big idea

• Mean: sum divided by count.
• Median: middle value of the ordered data.
• IQR: $Q_3-Q_1$, spread of the middle half.
• Outliers pull the mean but affect the median much less, so use median and IQR for skewed data.

Worked example

Data: $2,4,6,8,10,12,14,16$.

• Median: $\frac{8+10}{2}=9$.
• $Q_1=\frac{4+6}{2}=5$, $Q_3=\frac{12+14}{2}=13$.
• IQR $=13-5=8$.

Mean of $3,5,7,9,11$ is $\frac{35}{5}=7$.

Takeaways

• Order data before finding median and quartiles.
• Use median/IQR for skewed data.
• State the center and spread in context.