pg_0065
5.
Process Improvement
5.3.
Choosing an experimental design
5.3.3.
How do you select an experimental design.
5.3.3.3.
Full factorial designs
Full factorial designs in two levels
A design in
which every
setting of
every factor
appears with
every setting
of every other
factor is a
full factorial
design
A common experimental design is one with all input factors set at two
levels each. These levels are called `high' and `low' or `+1' and `-1',
respectively. A design with all possible high/low combinations of all
the input factors is called a full factorial design in two levels.
If there are k factors, each at 2 levels, a full factorial design has 2
k
runs.
TABLE 3.2 Number of Runs for a 2
k
Full Factorial
Number of Factors
Number of Runs
2
4
3
8
4
16
5
32
6
64
7
128
Full factorial
designs not
recommended
for 5 or more
factors
As shown by the above table, when the number of factors is 5 or
greater, a full factorial design requires a large number of runs and is
not very efficient. As recommended in the
Design Guideline Table
, a
fractional factorial design or a Plackett-Burman design is a better
choice for 5 or more factors.
5.3.3.3. Full factorial designs
http://www.itl.nist.gov/div898/handbook/pri/section3/pri333.htm [5/7/2002 4:01:47 PM]
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