#### Down the middle

What it does

Down the middle is designed to help learners explore the link between the mean of a dataset and the particular values that the dataset contains. By dragging the data values to different locations on the number line, you can see the effect on the mean.

The applet can also be set to operate in two dimensions; the aim here is to explore the link between the line of best fit (i.e. the regression line) and the particular values that the dataset contains.

Note: this applet has a simpler sister applet, Down the middle lite, which operates just in 1-D.

How to use it

When Down the middle is first opened, the data points are set to display in one dimension (1-D). From the drop-down menu, select the number of data points (2, 4, 8 or 16). Drag the points to left or right to see the effect on the mean (shown in blue). Change the number of points and repeat to see how sample size affects the behaviour of the mean when data values are altered.

Change the data points setting to 2-D to see the the data points displayed in two dimensions. From the drop-down menu, select the number of data points (2, 4, 8 or 16). Drag the points to different locations on the screen to see the effect on the line of best fit (shown in red). Change the number of points and repeat to see how sample size affects the direction and position of the regression line when data values are altered.

Note that in the 2-D setting the equation of the regression line and the value of the correlation coefficient (r) are also displayed.