Axis Scale for Matrix Scatterplots
You can change the axis scale on a matrix scatterplot to specify the range for the axis and whether the axis is linear or transformed. Any customizations you make to the axis scale options apply to all variables in the scatterplot.
How to Change the Axis Scale in a Matrix Scatterplot
- Select a scale axis on the matrix.
- If the Properties window is not already
displayed, from the menus choose:
- Use the Matrix Axis Scale tab to specify the axis scale options.
- Click Apply.
Using the Matrix Axis Scale Tab
If Auto is selected for the values, the Chart Editor automatically sets an appropriate value for each individual variable. Therefore, there might be different ranges for the different variables. On the other hand, when you deselect this check box and set the values manually, the values apply to all variables.
Minimum/Maximum. Change the range for all variables. The minimum and maximum values in the data for the chart are listed so that you can set a range that includes all of the data. These are the smallest and largest values across all variables. Other chart elements (for example, annotations) can be hidden when you change the range. If elements you expect to see aren't displayed, change the range back to automatic. If the scale is transformed, the range values are specified in the same units as the data values.
Major Increment. Specify the size of the increments between major ticks/labels. Beginning with the Minimum value, they occur at every increment specified by this number. In general, a division size that divides evenly into your range works best. For example, if your axis minimum is 0 and the maximum is 400, division sizes of 100, 50, or 25 would work well.
Origin. Specify the origin. An origin line is useful for matrix scatterplots with a transformed axis. The effect of changing the origin is most obvious when the data are far from the origin, because the transformation takes the origin into account. For example, assume that the axis is a log scale. The equation for the transformation is y'=log(y-origin). Therefore, if the data points are 1001, 1002, 1010 and the origin is 0, the transformation will look similar to an untransformed scale. However, if you change the origin to 1000, the transformation will look like a log scale as expected.
Display Line at Origin. Displays the axis at the value specified in the Origin text box.
Scale Type. Displays the data for all variables on a linear or transformed scale. A transformed scale is useful if the relationship between the independent and dependent variables is nonlinear. You can often transform these relationships into a straight-line relationship. Transformations help you to understand the data or to make assumptions necessary for statistical inference.
- Linear. Displays a linear, untransformed scale.
- Logarithmic. Displays a log-transformed scale. Optionally, you can enter a base for the log, which must be greater than 1. If Safe is selected, the transformation formula used for taking the log of an axis value x is not log(x). The Chart Editor uses a different formula so that it can take the log of nonpositive values. However, for values much greater than 1, it is essentially equivalent to log(x).
The safe log formula is:
sign(x) * log(1 + abs(x))
So, if you assume the axis value is –99, the result of the transformation is:
sign(-99) * log(1 + abs(-99)) = -1 * log(1 + 99) = -1 * 2 = -2
- Power. Displays an exponent-transformed scale. Optionally, you can enter a power. The default is 0.5, which would take the square root of the data.
Margins. Creates a margin around the data. You specify a percentage (0 to 50) of the inner frame to use for the margin. The margin appears perpendicular to the selected axis. For example, if you set the upper margin to 5% for the vertical axis, a margin whose thickness is 5% of the data area runs along the top of the data frame.