See the relationship between two variables before fitting a regression line.
In short: A scatter diagram plots paired data as points so you can see whether two variables are related. On the GDC you enter the x and y values in lists, turn on a statistics plot and display it with a suitable window. Draw it before running regression, to check that a straight line is a reasonable model.
| TI-84 Plus CE | Casio fx-CG50 and fx-CG100 | TI-Nspire CX | |
|---|---|---|---|
| Key sequence | 2nd → Y= (STAT PLOT) → Plot1 On → scatter icon → set Xlist and Ylist, then ZOOM → 9:ZoomStat. | In Statistics set GRPH → SET to Scatter, assign XList and YList, then DRAW. | On a Data & Statistics page click the x- and y-axis labels to assign the two variables. |
Tip: The scatter shape tells you whether a linear, quadratic or exponential model is sensible.
Tip: The scatter shape tells you whether a linear, quadratic or exponential model is sensible.
Tip: The scatter shape tells you whether a linear, quadratic or exponential model is sensible.
Here's a real IB-style question that uses exactly this technique.
Plot the points (1, 3), (2, 5), (3, 4), (4, 6), (5, 8) on a scatter diagram. Describe the correlation.
See the relationship between two variables before fitting a regression line. Before fitting a regression line, to check the relationship actually looks linear. Spotting an outlier or a non-linear pattern that a correlation coefficient alone would hide.
1. Enter the x-values in one list and the y-values in another (equal lengths). 2. 2nd → Y= (STAT PLOT) → Plot1 On → scatter icon → set Xlist and Ylist, then ZOOM → 9:ZoomStat. 3. Describe the correlation (positive/negative, strong/weak, linear or not) from the shape.
1. Enter the x-values in one list and the y-values in another (equal lengths). 2. In Statistics set GRPH → SET to Scatter, assign XList and YList, then DRAW. 3. Describe the correlation (positive/negative, strong/weak, linear or not) from the shape.
1. Enter the x-values in one list and the y-values in another (equal lengths). 2. On a Data & Statistics page click the x- and y-axis labels to assign the two variables. 3. Describe the correlation (positive/negative, strong/weak, linear or not) from the shape.
The scatter shape tells you whether a linear, quadratic or exponential model is sensible.
In the worked example on this page (2 marks, Paper 2), the marks are: M1: Points plotted correctly; A1: Positive (linear) correlation.
Questions that need this technique link back to this guide. Try one in practice mode, or see every GDC guide.