Objective: Minimize the number of defects (smaller the better)

Number of factors: 3 (Power, Heating Time, Feed Pressure)

Number of levels: 3 (see matrix)

Method: Taguchi Matrix L9 using Minitab

PowerHeating TimeFeed PressureRun 1Run 2Run 3

5531.5100

5562233

5592.5333

6032011

6062.5223

6091.5111

6532.5111

6561.5111

6592333

Analysis of Variance for S/N ratio

Source DFSeq SSAdj SSAdj MSFP

Power29.7599.7594.882.540.282

Heating Time2131.195131.19565.59834.180.028

Feed pressure2103.042103.04251.52126.840.036

Residual Error23.8393.8391.919

Total8247.836

Response Table for S/N ratioLevelPowerHeating Time Feed Pressure

1-4.4752.1771.59

2-1.924-5.395-5.478

3-3.181-6.362-5.692

Delta2.5518.5397.282

Rank312

Prediction

Selected the optimum settings from the Main effects plot and response table for S/N ratios

PowerHeating Time Feed Pressure

6031.5

Predicted values:

S/N ratioMean

8.23011-0.55556

Question:

The objective was to minimize the number of defects. I selected the optimum settings from my DOE and predicted the results. What does a mean of -0.55556 imply? Does that mean the number of defects will be less than zero? Please advice.