|
WHLM will
also let us examine plots for individual level-2 units by
just using the level-1 equation instead of the entire model.
For this example, we will be using the vocabulary data, vocab.mdm,
and have run the following model:
To
perform level-1 equation graphing
After the model is run, select
Graph Equations...Level-1 equation graphing from the
File menu, which will give us the following dialog
box.
There are
three options for the number of groups: (a) First ten groups;
(b) Random sample of spec'd prob (specified probability)
and (c) All groups (n = total number of groups) for
users to choose from in the Number of groups drop-down
list box. The selection of option (b) requires the user to
specify the proportion or percent of the level-2 units to
be included.
Select an X focus variable.
In our example, we want the age of the child in months minus
12 to be the X focus. Choose AGE12 from the X focus
drop-down list box.
Select
the number of groups. We will include all the children. Choose
All groups (n=22) in the Number of groups drop-down
list box.
Specify
the relationship between the transformed and the original
variable. The transformed variable is AGE12S and the original
variable is AGE12. Click 1 in the Categories/ transforms/interactions
section and select power of x/z for polynomial relationships.
A Equation Graphing - power dialog box will open. Select
AGE12S from the drop-down list box to the left of the equal
sign. AGE12 will appear in the drop-down list box as it is
the only level-1 variable left. Enter 2 in the text box for
the power to be raised. Click OK.
The ranges for x- and y-axis
(the default values are those computed from the data), legend
and graph titles, and selection of screen color can be changed
by clicking Range/Legend/Color to obtain the Range/Legend/Color
dialog box.
Click the Other settings
button and click the selection button for Smooth in
For continuous x section to display a set of smooth
curves. Click OK.
Click OK and we get the
following figure that shows vocabulary size accelerates during
the second year of life. Note that the individual trajectories,
as expected, are “smoother” than in comparable
data-based graphs.
To
include a level-2 classification variable
Click Graph Settings
on the menu bar to open the Level-1 equation Graphing dialog
box. Choose MALE from the Z-focus drop-down list box
as the level-2 classification variable and click OK.
A colored version of the graph
indicates that girls on average have a greater acceleration
rate in vocabulary growth over the course of the study.
 
|
Model
based graphs: Level-1 equation modeling