Scatterplots

A scatterplot is the most effective way to display the relation between two quantitative variables. 
 
A scatterplot is a graphical representation of two quantitative variables on the same coordinate system.  The explanatory, or independent variable, is plotted on the horizontal axis (the x-axis).  The response variable, or dependent variable, is plotted on the vertical axis (the y-axis).  If either variable is a measurement of time, this variable should be plotted on the horizontal axis, or x-axis. 

The scatterplots are used to interpret the relationship between the two variables by looking for an overall pattern.  The pattern should give you information regarding direction, form, and strength.  The direction indicates a positive association when large values of the explanatory variable accompany large values of the response variables, while small values of the explanatory variable accompany small values of the response variable.  The direction indicates a negative association when large values of the explanatory variable accompany small values of the response variables, while small values of the explanatory variable accompany large values of the response variable. 

The form of the scatterplot includes whether there are clusters of data plots versus a more uniform pattern.  Clusters tends to indicate special circumstances surrounding the data pairs, such as age differences, testing differences, and/or grade level differences. 

The strength of the scatter plot is indicated by the roundness or the more linear shape to the plot.  The more round the scatterplot, the weaker the relationship between the data.  The more linear the scatterplot, the stronger the relationship between the data. 

Both the TI-82 and the TI-83 graphing calculators have the option to create scatterplots as 'dotplots' of the coordinate pairs of data and as a 'XY line' which plots the data pairs and then joins these points with a line. 

The directions for each type of scatterplot are on the separate pages.