M4.7.8 For the adult
Telling the truth with data
A chart shows one tall bar and one short bar, but the two numbers are almost the same. Is the chart telling the truth?
What this chapter teaches
A chart can mislead without any wrong number, for example by starting a bar chart above zero. An average can mislead when an outlier pulls the mean away from the typical value. A fair comparison of two groups gives a measure of the middle and a measure of the spread, with units.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why is a bar chart that starts at 50 instead of 0 misleading?
- Why might the median be a better average than the mean for journey times that include one very long journey?
- Two groups have the same median. What else would you check before saying they are alike?
After the chapter, the learner can
- Spot a misleading graph or a misleading average
- Write a short report that compares two groups
What they copy into their notebook
Check the scale: a cut axis misleads. An outlier pulls the mean, so use the median. To compare groups, give the median and the IQR, with the units.