A team of researchers collects data about factors that affect a quality characteristic of baked pretzels. Variables include process settings, like Mix Tool, and grain properties, like Flour Protein.
As part of the initial exploration of the data, the researchers decide to use Discover Key
Predictors to compare models by sequentially removing unimportant predictors to identify key predictors. The researchers hope to identify key predictors that have large effects on the quality characteristic and to gain more insights into the relationships among the quality characteristic and the key predictors.
Interpret the results
For this analysis, Minitab Statistical Software compares 28 models. The number of steps is less than the maximum number of steps because the Foam Stability predictor has an importance score of 0 in the first model, so the algorithm eliminates 2 variables in the first step. The asterisk in the Model column of the Model Evaluation table shows that the model with the smallest value of the average –loglikelihood statistic is model 23. The results that follow the model evaluation table are for model 23.
Although model 23 has the smallest value of the average –loglikelihood statistic, other models have similar values. The team can click Select an Alternative Model to produce results for other models from the Model Evaluation table.
In the results for Model 23, the Average –Loglikelihood vs. Number of Trees Plot shows that the optimal number of trees is almost the number of trees in the analysis. The team can click Tune Hyperparameters to Identify a Better Model to increase the number of trees and to see whether changes to other hyperparameters improve the performance of the model.
The Relative Variable Importance graph plots the predictors in order of their effect on model improvement when splits are made on a predictor over the sequence of trees. The most important predictor variable is Mix Time. If the importance of the top predictor variable, Mix Time, is 100%, then the next important variable, Kiln Temperature, has a contribution of 93.9%. This means that Kiln Temperature is 93.9% as important as Mix Time.
Use the partial dependency plots to gain insight into how the important variables or pairs of variables affect the predicted response. The response values on the 1/2 log scale are the predictions from the model. The partial dependence plots show whether the relationship between the response and a variable is linear, monotonic, or more complex.
The one predictor partial dependence plots show that medium values for Mix Time, Kiln Temperature and Bake Time increase the odds of an acceptable pretzel. A medium value of Dry Time decreases the odds of an acceptable pretzel. The researchers can click Select More Predictors to Plot to produce plots for other variables.
The two-predictor partial dependence plot of Mix Time and Kiln Temperature shows a more complex relationship between the two variables and the response. While medium values of Mix Time and Kiln Temperature increase the odds of an acceptable pretzel, the plot shows that the best odds occur when both variables are at medium values. The researchers can click Select More Predictors to Plot to produce plots for other pairs of variables.
TreeNet® Classification: Acceptable P vs Flour Protei, Water, Mix Time, ...
Method
Criterion for selecting optimal number of trees Maximum loglikelihood
Model validation 70/30% training/test sets
Learning rate 0.05
Subsample selection method Completely random
Subsample fraction 0.5
Maximum terminal nodes per tree 6
Minimum terminal node size 3
Number of predictors selected for node splitting Total number of predictors = 29
Rows used 5000
Binary Response Information
Training Test
Variable Class Count % Count %
Acceptable Pretzel 1 (Event) 2160 61.82 943 62.62
0 1334 38.18 563 37.38
All 3494 100.00 1506 100.00
One Predictor Partial Dependence Plots
Select More Predictors to Plot...
Two Predictor Partial Dependence Plots
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TreeNet® Classification - Discover Key Predictors: Acceptable P vs Flour Protei, Water, ...
Predictor Elimination Plot
Model Selection by Eliminating Unimportant Predictors
Test
Optimal
Number Average Number of
Model of Trees -Loglikelihood Predictors Eliminated Predictors
1 268 0.273936 29 None
2 268 0.274186 27 Foam Stability, Bulk Density
3 234 0.273843 26 Least Gelation Concentration
4 233 0.274350 25 Oven Mode 2
5 232 0.274943 24 Kiln Method
6 273 0.275553 23 Oven Mode 1
7 244 0.274811 22 Mix Speed
8 268 0.274258 21 Oven Mode 3
9 272 0.274185 20 Resting Surface
10 232 0.274077 19 Bake Temperature 3
11 287 0.273598 18 Mix Tool
12 227 0.274358 17 Bake Temperature 1
13 276 0.275374 16 Rest Time
14 272 0.276082 15 Water
15 268 0.275595 14 Caustic Concentration
16 268 0.277810 13 Swelling Capacity
17 253 0.276436 12 Emulsion Stability
18 231 0.276159 11 Emulsion Activity
19 268 0.273537 10 Water Absorption Capacity
20 260 0.273455 9 Oil Absorption Capacity
21 299 0.272848 8 Flour Protein
22 278 0.272629 7 Foam Capacity
23* 299 0.267184 6 Flour Size
24 297 0.288621 5 Bake Temperature 2
25 234 0.330342 4 Dry Time
26 290 0.305993 3 Gelatinization Temperature
27 245 0.534345 2 Bake Time
28 146 0.599837 1 Kiln Temperature
The algorithm removed one predictor and any predictors with 0 importance at
each step.
* Selected model has minimum average -loglikelihood. Output for the selected
model follows.
One Predictor Partial Dependence Plots
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Two Predictor Partial Dependence Plots
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TreeNet® Classification: Acceptable P vs Mix Time, Bake Time, Dry Time, ...
Model Summary
Total predictors 6
Important predictors 6
Number of trees grown 300
Optimal number of trees 299
Statistics Training Test
Average -loglikelihood 0.2418 0.2672
Area under ROC curve 0.9661 0.9412
95% CI (0.9608, 0.9713) (0.9295, 0.9529)
Lift 1.6176 1.5970
Misclassification rate 0.0970 0.0963
One Predictor Partial Dependence Plots
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Two Predictor Partial Dependence Plots
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TreeNet® Classification: Acceptable P vs Mix Time, Bake Time, Dry Time, ...
Confusion Matrix
Predicted Class (Training) Predicted Class (Test)
Actual Class Count 1 0 % Correct Count 1 0 % Correct
1 (Event) 2160 1942 218 89.91 943 846 97 89.71
0 1334 121 1213 90.93 563 48 515 91.47
All 3494 2063 1431 90.30 1506 894 612 90.37
Assign a row to the event class if the event probability for the row exceeds
0.5.
Statistics Training (%) Test (%)
True positive rate (sensitivity or power) 89.91 89.71
False positive rate (type I error) 9.07 8.53
False negative rate (type II error) 10.09 10.29
True negative rate (specificity) 90.93 91.47
Misclassification
Training Test
Actual Class Count Misclassed % Error Count Misclassed % Error
1 (Event) 2160 218 10.09 943 97 10.29
0 1334 121 9.07 563 48 8.53
All 3494 339 9.70 1506 145 9.63
Assign a row to the event class if the event probability for the row exceeds
0.5.
One Predictor Partial Dependence Plots
Select More Predictors to Plot...
Two Predictor Partial Dependence Plots
Select More Predictors to Plot...