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With rdExpert, you can have mixed level designs and upto fifty factors.
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With L18, one will get lot more information about 8 factors.
Regards
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You can use Taguchi approach.  But instead of Studying two levels, try three levels and run L18 for 8 factors.  You can test remaining factors later.
Regards.

Toyota  had a weapon Genichi Taguchi working with them from 1970s.  So they did not need any other certifications.
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