First of all you should tel us a priory knowledge about outcome?
If Second order model of outcome is satisfactory then you should apply CENTRAL COMPOSITE ROTATABLE DESIGNS (CCRD) for k=2 with 5 replica at NULL factor level, which design plan is:
TABLE 2.147 CCRD
Design of experiment
matrix
No of
exper.
X1 (factor
level)
X2 (factor
level)
1
+
+
2
–
+
3
+
–
4
–
–
5
-1,414
0
6
+1,414
0
7
0
-1,414
8
0
+1,414
9
0
0
10
0
0
11
0
0
12
0
0
13
0
0
So yu should have 13 experiments in order to get second order regression model for outcam with high confidence. The question is :
– ar you restricted with number of experiment ( time, expenses etc.)?
if answer is no then I propose CENTRAL COMPOSITE ROTATABLE DESIGNS (CCRD) for k=2 with 5 replica at NULL factor level.
