Read the median, quartiles, range and any outliers - and draw the box plot a question asks for.
In short: A box-and-whisker plot displays the minimum, lower quartile, median, upper quartile and maximum of a data set. The GDC draws it from a list once you set up a statistics plot, and the same menu gives the quartile values. Use it to compare spread and to spot outliers, which some models mark automatically.
| TI-84 Plus CE | Casio fx-CG50 and fx-CG100 | TI-Nspire CX | |
|---|---|---|---|
| Key sequence | 2nd → Y= (STAT PLOT) → choose the box-plot icon, then ZOOM → 9:ZoomStat. 1-Var Stats also lists Q1, Med, Q3. | In Statistics set GRPH → SET to MedBox, then DRAW; 1-VAR also lists the quartiles. | On a Data & Statistics page add the variable to the x-axis, then menu → Plot Type → Box Plot. |
Tip: Box plots make comparing the spread of two data sets very quick.
Tip: Box plots make comparing the spread of two data sets very quick.
Tip: Box plots make comparing the spread of two data sets very quick.
Here's a real IB-style question that uses exactly this technique.
For the data set 2, 4, 5, 7, 8, 10, 11, 14, find the median, the lower quartile Q1 and the upper quartile Q3.
Read the median, quartiles, range and any outliers - and draw the box plot a question asks for. A question asks you to draw a box-and-whisker plot from raw data. Finding the quartiles and interquartile range (IQR) to describe spread or identify outliers.
1. Enter the data in a list (and frequencies in a second list if grouped). 2. 2nd → Y= (STAT PLOT) → choose the box-plot icon, then ZOOM → 9:ZoomStat. 1-Var Stats also lists Q1, Med, Q3. 3. IQR = Q3 − Q1. Outliers lie beyond Q1 − 1.5×IQR or Q3 + 1.5×IQR.
1. Enter the data in a list (and frequencies in a second list if grouped). 2. In Statistics set GRPH → SET to MedBox, then DRAW; 1-VAR also lists the quartiles. 3. IQR = Q3 − Q1. Outliers lie beyond Q1 − 1.5×IQR or Q3 + 1.5×IQR.
1. Enter the data in a list (and frequencies in a second list if grouped). 2. On a Data & Statistics page add the variable to the x-axis, then menu → Plot Type → Box Plot. 3. IQR = Q3 − Q1. Outliers lie beyond Q1 − 1.5×IQR or Q3 + 1.5×IQR.
Box plots make comparing the spread of two data sets very quick.
In the worked example on this page (4 marks, Paper 2), the marks are: M1: Enter the data as a one-variable list; A1: Median = 7.5; A1: Q1 = 4.5; A1: Q3 = 10.5.
Questions that need this technique link back to this guide. Try one in practice mode, or see every GDC guide.