JMP Analysis of a Split Plot Design
The data are from an experiment run to evaluate the cut off time for lawnmower engines. There
are two factors of interest: the whole plot factor (Manufacturer) and the subplot factor (Speed).
The machines act as blocks for the part of the experiment involving the Speed factor. There are
four columns in the JMP Data Table: Manufacturer, Speed, Machine and Cutoff Time.
Manufacturer
A
A
A
A
A
A
A
A
A
A
A
A
B
B
B
B
B
B
B
B
B
B
B
B
Speed
Low
Low
High
High
Low
Low
High
High
Low
Low
High
High
Low
Low
High
High
Low
Low
High
High
Low
Low
High
High
Machine
1
1
1
1
2
2
2
2
3
3
3
3
4
4
4
4
5
5
5
5
6
6
6
6
Cutoff Time
211
230
278
278
184
188
249
272
216
232
275
271
205
217
247
251
169
168
239
252
200
187
261
242
You will need to use the Fit Model platform
• The response variable, Y, is Cutoff Time
• In the Construct Model Effects’ box, Add Manufacturer. Add Machine.
• Highlight Machine in the Construct Model Effects’ box and highlight Manufacturer in the
Select Columns box. Click on Nest. This should change Machine to Machine nested
within Manufacturer: Machine[Manufacturer].
• Add Speed.
• Add a Manufacturer*Speed interaction by highlighting both Manufacturer and Speed in
the Select Columns box and clicking on Cross.
• Be sure to ask for a Minimal Report and click on OK.
The output from this analysis appears below. Note that the F-Ratio for testing for a difference
between Manufacturers uses the incorrect error term.
Response Cutoff Time
Summary of Fit
RSquare
RSquare Adj
Root Mean Square Error
Mean of Response
Observations (or Sum Wgts)
0.925432
0.892808
11.50226
230.0833
24
Analysis of Variance
Source
DF
Model
7
Error
16
C. Total
23
Sum of Squares
26271.000
2116.833
28387.833
Mean Square
3753.00
132.30
Effect Tests
Source
Manufacturer
Machine[Manufacturer]
Speed
Manufacturer*Speed
Nparm
1
4
1
1
Sum of Squares
2521.500
2852.833
20886.000
10.667
DF
1
4
1
1
F Ratio
28.3669
Prob > F
<.0001
F Ratio
19.0587
5.3908
157.8660
0.0806
Prob > F
0.0005
0.0061
<.0001
0.7801
Go back to the Construct Model Effects’ box and highlight Machine[Manufacturer]. Click on
the red arrow to the right of Attributes and select Random Effect. Change the Method from
REML (Recommended) to EMS (Traditional). This should produce the output below.
Response Cutoff Time
Analysis of Variance
Source
DF
Model
7
Error
16
C. Total
23
Sum of Squares
26271.000
2116.833
28387.833
Tests wrt Random Effects
Source
Manufacturer
Machine[Manufacturer]&Random
Speed
Manufacturer*Speed
Mean Square
3753.00
132.30
SS
MS
2521.5 2521.5
2852.83 713.208
20886
20886
10.6667 10.6667
F Ratio
28.3669
Prob > F
<.0001
DF
1
4
1
1
F Ratio
3.5354
5.3908
157.8660
0.0806
Prob > F
0.1332
0.0061
<.0001
0.7801