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If I have two classifiers for example Neural network and support vector machine , now I want to know what would be the best way to identify which is good classifier , should it be based on classification accuracy or by analyzing confusion matrix or average precision score, f1 score etc.

I have seen in most of the papers related to image classification that they only take classification accuracy as the parameter to compare different models.

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  • $\begingroup$ You can check the link below and the accepted answer: stats.stackexchange.com/questions/45851/… $\endgroup$ – Taimur Islam Feb 27 '18 at 3:50
  • $\begingroup$ Binary classification, multiclass or multilabel? $\endgroup$ – ncasas Mar 28 '18 at 15:46
  • $\begingroup$ Multi-label classification @ncasas $\endgroup$ – Boris Mar 28 '18 at 15:47
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Since the problem you are trying to tacle is image classification, then classification accuracy is the appropriate measure of comparison. Also you could consider the Precision, Recall and F1 metrics (for multi-class problems). See below there is description of an extension about these multi-class metrics.

A Simple Generalisation of the Area Under the ROC Curve for Multiple Class Classification Problems

Another appropriate metric is AUC/ROC, which has to be extended cosnidering the multi-class case. See the link below

Receiver Operating Characteristic (ROC)

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  • $\begingroup$ but can I plot average or macro ROC as given in scikit learn $\endgroup$ – Boris May 28 '18 at 2:20
  • $\begingroup$ Yes you can extend ROC curve and ROC area to multi-class classification problems. Check the link below scikit-learn.org/stable/auto_examples/model_selection/… $\endgroup$ – Christos Karatsalos May 28 '18 at 8:39
  • $\begingroup$ Yes But if I have to compare 3 classifiers then I have to plot individual class Roc plot. Although I wanted to have a single ROC plot to compare 3 different classifiers in one plot $\endgroup$ – Boris May 28 '18 at 16:05
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One thing to also consider is the effect of false positive/negative. Without that info, it will be very difficult to help you to use the right metric.

For instance, a model for approving car loans vs. a model for screening cancer would probably need to be assessed quite differently.

The Wikipedia article is a great starting point.

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Disclaimer, Many evaluation parameters and test-benches had been introduced for different case studies. The answer of your question that is what is the best parameter in my case, depends on different aspects such as the field of your problem (medical image processing, speech processing, and etc.), the type of your dataset (balance or imbalance), and the type of your classification (binary or multi-class).

PyCM is a Python module which gives you a wide variety of parameters in order to analyse your confusion matrix and compare different CMs through various parameters and testbenches.

There is a simple code for using this module:

>>> from pycm import *
>>> y_actu = [2, 0, 2, 2, 0, 1, 1, 2, 2, 0, 1, 2] # or y_actu = numpy.array([2, 0, 2, 2, 0, 1, 1, 2, 2, 0, 1, 2])
>>> y_pred = [0, 0, 2, 1, 0, 2, 1, 0, 2, 0, 2, 2] # or y_pred = numpy.array([0, 0, 2, 1, 0, 2, 1, 0, 2, 0, 2, 2])
>>> cm = ConfusionMatrix(actual_vector=y_actu, predict_vector=y_pred) # Create CM From Data
>>> cm.classes
[0, 1, 2]
>>> cm.table
{0: {0: 3, 1: 0, 2: 0}, 1: {0: 0, 1: 1, 2: 2}, 2: {0: 2, 1: 1, 2: 3}}
>>> print(cm)
Predict          0        1        2        
Actual
0                3        0        0        
1                0        1        2        
2                2        1        3        




Overall Statistics : 

95% CI                                                           (0.30439,0.86228)
Bennett_S                                                        0.375
Chi-Squared                                                      6.6
Chi-Squared DF                                                   4
Conditional Entropy                                              0.95915
Cramer_V                                                         0.5244
Cross Entropy                                                    1.59352
Gwet_AC1                                                         0.38931
Joint Entropy                                                    2.45915
KL Divergence                                                    0.09352
Kappa                                                            0.35484
Kappa 95% CI                                                     (-0.07708,0.78675)
Kappa No Prevalence                                              0.16667
Kappa Standard Error                                             0.22036
Kappa Unbiased                                                   0.34426
Lambda A                                                         0.16667
Lambda B                                                         0.42857
Mutual Information                                               0.52421
Overall_ACC                                                      0.58333
Overall_RACC                                                     0.35417
Overall_RACCU                                                    0.36458
PPV_Macro                                                        0.56667
PPV_Micro                                                        0.58333
Phi-Squared                                                      0.55
Reference Entropy                                                1.5
Response Entropy                                                 1.48336
Scott_PI                                                         0.34426
Standard Error                                                   0.14232
Strength_Of_Agreement(Altman)                                    Fair
Strength_Of_Agreement(Cicchetti)                                 Poor
Strength_Of_Agreement(Fleiss)                                    Poor
Strength_Of_Agreement(Landis and Koch)                           Fair
TPR_Macro                                                        0.61111
TPR_Micro                                                        0.58333

Class Statistics :

Classes                                                          0                       1                       2                       
ACC(Accuracy)                                                    0.83333                 0.75                    0.58333                 
BM(Informedness or bookmaker informedness)                       0.77778                 0.22222                 0.16667                 
DOR(Diagnostic odds ratio)                                       None                    4.0                     2.0                     
ERR(Error rate)                                                  0.16667                 0.25                    0.41667                 
F0.5(F0.5 score)                                                 0.65217                 0.45455                 0.57692                 
F1(F1 score - harmonic mean of precision and sensitivity)        0.75                    0.4                     0.54545                 
F2(F2 score)                                                     0.88235                 0.35714                 0.51724                 
FDR(False discovery rate)                                        0.4                     0.5                     0.4                     
FN(False negative/miss/type 2 error)                             0                       2                       3                       
FNR(Miss rate or false negative rate)                            0.0                     0.66667                 0.5                     
FOR(False omission rate)                                         0.0                     0.2                     0.42857                 
FP(False positive/type 1 error/false alarm)                      2                       1                       2                       
FPR(Fall-out or false positive rate)                             0.22222                 0.11111                 0.33333                 
G(G-measure geometric mean of precision and sensitivity)         0.7746                  0.40825                 0.54772                 
LR+(Positive likelihood ratio)                                   4.5                     3.0                     1.5                     
LR-(Negative likelihood ratio)                                   0.0                     0.75                    0.75                    
MCC(Matthews correlation coefficient)                            0.68313                 0.2582                  0.16903                 
MK(Markedness)                                                   0.6                     0.3                     0.17143                 
N(Condition negative)                                            9                       9                       6                       
NPV(Negative predictive value)                                   1.0                     0.8                     0.57143                 
P(Condition positive)                                            3                       3                       6                       
POP(Population)                                                  12                      12                      12                      
PPV(Precision or positive predictive value)                      0.6                     0.5                     0.6                     
PRE(Prevalence)                                                  0.25                    0.25                    0.5                     
RACC(Random accuracy)                                            0.10417                 0.04167                 0.20833                 
RACCU(Random accuracy unbiased)                                  0.11111                 0.0434                  0.21007                 
TN(True negative/correct rejection)                              7                       8                       4                       
TNR(Specificity or true negative rate)                           0.77778                 0.88889                 0.66667                 
TON(Test outcome negative)                                       7                       10                      7                       
TOP(Test outcome positive)                                       5                       2                       5                       
TP(True positive/hit)                                            3                       1                       3                       
TPR(Sensitivity, recall, hit rate, or true positive rate)        1.0                     0.33333                 0.5  

>>> cm.matrix()
Predict          0        1        2        
Actual
0                3        0        0        
1                0        1        2        
2                2        1        3        

>>> cm.normalized_matrix()
Predict          0              1              2              
Actual
0                1.0            0.0            0.0            
1                0.0            0.33333        0.66667        
2                0.33333        0.16667        0.5 
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