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. 2019 Aug 19;5(8):e02298. doi: 10.1016/j.heliyon.2019.e02298

Table 1.

The level of the independent variables used in RSM.

Independent variables Unit Code Actual levels of coded factor
-1 0 +1
Carbon concentration % A 1 2 3
Nitrogen concentration % B 0.5 1 1.5
Moisture content % C 45 60 75
Incubation time h D 24 60 96