Advanced tutorial on bias detection in dalex¶

In this tutorial, we cover the more advanced aspects of the fairness module in dalex. For the introduction, see Fairness module in dalex example.

import pandas as pd 
import numpy as np 
{"pd": pd.__version__, "np": np.__version__}

{'pd': '1.2.4', 'np': '1.19.5'}

Data¶

Firstly we load the data, which is based on the famous ProPublica study on the COMPAS recidivism algorithm.

compas = pd.read_csv("https://raw.githubusercontent.com/propublica/compas-analysis/master/compas-scores-two-years.csv")

To get a clearer picture, we will only use a few columns of the original data frame.

compas = compas[["sex", "age", "age_cat", "race", "juv_fel_count", "juv_misd_count",
                 "juv_other_count", "priors_count", "c_charge_degree", "is_recid",
                 "is_violent_recid", "two_year_recid"]]
compas.head()

As we can see, we have a relatively compact pandas.DataFrame. The target variable is two_year_recid which denotes if a particular person will re-offend in the next two years. For this tutorial, we will use scikit-learn models, but these methods are model-agnostic.

age_cat = compas.age_cat
compas = compas.drop("age_cat", axis =1)

compas.dtypes

sex                 object
age                  int64
race                object
juv_fel_count        int64
juv_misd_count       int64
juv_other_count      int64
priors_count         int64
c_charge_degree     object
is_recid             int64
is_violent_recid     int64
two_year_recid       int64
dtype: object

Models¶

Like in the previous example, we will make 3 basic predictive models without the hyperparameter tuning.

from sklearn.compose import ColumnTransformer
from sklearn.pipeline import Pipeline
from sklearn.preprocessing import OneHotEncoder, StandardScaler
from sklearn.model_selection import train_test_split

# classifiers
from sklearn.tree import DecisionTreeClassifier
from sklearn.ensemble import RandomForestClassifier
from sklearn.linear_model import LogisticRegression

X_train, X_test, y_train, y_test = train_test_split(compas.drop("two_year_recid", axis =1),
                                                    compas.two_year_recid,
                                                    test_size=0.3,
                                                    random_state=123)

categorical_features = ['sex', 'race', 'c_charge_degree']
categorical_transformer = Pipeline(steps=[
    ('onehot', OneHotEncoder(handle_unknown='ignore'))
])

numerical_features = ["age", "priors_count"]
numerical_transformer = Pipeline(steps=[
    ('scale', StandardScaler())
])

preprocessor = ColumnTransformer(transformers=[
        ('cat', categorical_transformer, categorical_features),
        ('num', numerical_transformer, numerical_features)
])

clf_tree = Pipeline(steps=[
    ('preprocessor', preprocessor),
    ('classifier', DecisionTreeClassifier(max_depth=7, random_state=123))
])

clf_forest = Pipeline(steps=[
    ('preprocessor', preprocessor),
    ('classifier', RandomForestClassifier(n_estimators=200, max_depth=7, random_state=123))
])

clf_logreg = Pipeline(steps=[
    ('preprocessor', preprocessor),
    ('classifier', LogisticRegression())
])


clf_logreg.fit(X_train, y_train)
clf_forest.fit(X_train, y_train)
clf_tree.fit(X_train, y_train)

Pipeline(steps=[('preprocessor',
                 ColumnTransformer(transformers=[('cat',
                                                  Pipeline(steps=[('onehot',
                                                                   OneHotEncoder(handle_unknown='ignore'))]),
                                                  ['sex', 'race',
                                                   'c_charge_degree']),
                                                 ('num',
                                                  Pipeline(steps=[('scale',
                                                                   StandardScaler())]),
                                                  ['age', 'priors_count'])])),
                ('classifier',
                 DecisionTreeClassifier(max_depth=7, random_state=123))])

Explainers¶

Now, we need to create Explainer objects with the help of dalex.

import dalex as dx
dx.__version__

'1.4.0'

exp_logreg = dx.Explainer(clf_logreg, X_test, y_test)

Preparation of a new explainer is initiated

  -> data              : 2165 rows 10 cols
  -> target variable   : Parameter 'y' was a pandas.Series. Converted to a numpy.ndarray.
  -> target variable   : 2165 values
  -> model_class       : sklearn.linear_model._logistic.LogisticRegression (default)
  -> label             : Not specified, model's class short name will be used. (default)
  -> predict function  : <function yhat_proba_default at 0x000001AB7FE380D0> will be used (default)
  -> predict function  : Accepts only pandas.DataFrame, numpy.ndarray causes problems.
  -> predicted values  : min = 0.0421, mean = 0.444, max = 0.988
  -> model type        : classification will be used (default)
  -> residual function : difference between y and yhat (default)
  -> residuals         : min = -0.978, mean = 2.17e-05, max = 0.92
  -> model_info        : package sklearn

A new explainer has been created!

exp_tree = dx.Explainer(clf_tree, X_test, y_test, verbose=False)
exp_forest = dx.Explainer(clf_forest, X_test, y_test, verbose=False)

model performance¶

pd.concat([exp.model_performance().result for exp in [exp_logreg, exp_tree, exp_forest]])

permutation-based variable importance¶

Now, we will use one of the dalex methods to assess the Variable Importance of these models

exp_tree.model_parts().plot(objects=[exp_forest.model_parts(), exp_logreg.model_parts()])

	sex	age	age_cat	race	juv_misd_count	juv_other_count	priors_count	c_charge_degree	is_recid	is_violent_recid	two_year_recid
0	Male	69	Greater than 45	Other	0	0	0	F	0	0	0
1	Male	34	25 - 45	African-American	0	0	0	F	1	1	1
2	Male	24	Less than 25	African-American	0	1	4	F	1	0	1
3	Male	23	Less than 25	African-American	1	0	1	F	0	0	0
4	Male	43	25 - 45	Other	0	0	2	F	0	0	0

	recall	precision	f1	accuracy	auc
LogisticRegression	0.545265	0.659119	0.596811	0.672979	0.706204
DecisionTreeClassifier	0.516129	0.639175	0.571100	0.655889	0.688712
RandomForestClassifier	0.546306	0.649752	0.593556	0.667898	0.712737