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Poisson Regressionp-value |
The p-values test whether or not an observed relationship is statistically significant. The p-values in the deviance table are for the likelihood ratio tests. The likelihood ratio tests are more accurate for small samples than Wald approximation tests. You need to:
1 Identify the p-value at the top of the deviance table. This p-value tells you if there is a significant association between at least one predictor and the response by testing whether all slopes are equal to zero.
2 Compare this p-value to your a-level. If the p-value is less than or equal to the a-level you have selected, the association is significant. A commonly used a-level is 0.05.
3 If you concluded in step 2 that there is at least one significant predictor, identify the p-value for each term in the model. These p-values tell you whether or not there is a statistically significant association between a particular predictor variable and the response.
4 Compare the individual p-values to your a-level: If a p-value is less than or equal to the a-level you have selected, the association is significant.
Example Output |
Deviance Table
Source DF Adj Dev Adj Mean Chi-Square P-Value Regression 3 56.670 18.8900 56.67 0.000 Temperature 1 38.800 38.8000 38.80 0.000 Hours Since Cleanse 1 4.744 4.7444 4.74 0.029 Size of Screw 1 13.126 13.1256 13.13 0.000 Error 32 31.607 0.9877 Total 35 88.277 |
Interpretation |
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For the resin defect data, the p-value for testing that all slopes are zero is 0.000. Assume an a-level of 0.05. Because 0.000 is less than 0.05, the quality analysts conclude that there is a significant relationship between the response and at least one of the predictor variables.
Now look at the p-values for each predictor. If the a-level is 0.05, the temperature, the hours since cleanse, and the size of the screw are all statistically signficant.