What is the criteria of determination of low and high value in Plackett-Burman (PB) designs?
The answer is in the article
http://link.springer.com/article/10.1007/BF02269627
The "low" and "high" values depend upon what you are testing. For example, if I am testing recipes for chocolate chip cookies, I can test the amount of flour, white sugar, brown sugar, butter, eggs, bake temp and bake time. I can use the original recipe and set my high values as the recipe plus 10% and the low values as recipe minus 10%. Since I am looking to improve something that is already good, I won't want to stray to far away, initially.
If I am working with something new, I should be a little more adventurous. However, I need to know what I am working with. If we are talking about polymers, then I would want to look at temps that are high enough to melt the polymers but not so hot that the polymers decompose/"burn". If I am dealing with the best temp to grow an algae culture, I would choose temps that are a bit warmer than normal and colder than normal. If I want to grow bacteria from the human gut, I wouldn't change the temp more than body temp +/-5C. And that might be too much.
If you are dealing with categorical data, like solvent to use: Methanol vs Acetone. It does not matter which one you put has the high or the low.
Hope this helps.
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