Spikes

You can display a line from each data point to another location in the chart. These lines are called spikes and apply to simple and 3-D scatterplots. Spikes can help emphasize the difference between a data point and some other point of interest. For example, you might add spikes to see which point is furthest from the centroid. Spikes are also useful when printing a 3-D scatterplot.

You can also display spikes from a fit line to the data points. See the topic Fit Lines for more information.

How to Display Spikes on a Scatterplot

1. Select all data markers the scatterplot. You cannot display spikes for only one category.
2. From the menus choose:

   Edit > Properties

3. Use the Spikes tab to specify a location for the spikes.
4. Click Apply.

Using the Spikes Tab

None. Do not display spikes.

Floor. Display spikes from each point to the x axis in a 2-D scatterplot or the plane of the x and z axes in a 3-D scatterplot.

Origin. Display spikes from each point to the origin of the axes. The origin is the point at which all of the axes intersect (0,0,0).

Centroid. Display spikes from each point to the centroid of all the points. The coordinates of the centroid are the weighted means for each axis. A missing value in any one of the variables excludes the case from the calculation. Changing the scale does not affect the calculation of the centroid.