Morris Sensitivity Analysis

Link to API Reference: MorrisSensitivity

See the backing repository for Morris here.

Summary

Also known as the Morris method[1], this is a one-step-at-a-time (OAT) global sensitivity analysis where only one input has its level (discretized value) adjusted per run. Relative to other sensitivity analysis algorithms, the Morris method is fast (fewer model executions) but comes at the cost of not being able to differentiate non-linearities with interactions. This is commonly used for screening which inputs are important enough for further analysis. The implementation uses SALib[2] for its Morris method.

How it Works

The gsa-module package has a good conceptual overview of the Morris method for screening here.

The SALib package describes what sensitivity analysis is, and the steps required in conducting it at a basic level here.

The conceiving paper for Morris method[1] can be found here.

Code Example

The following code will train a blackbox pipeline for the breast cancer dataset. Aftewards it will interpret the pipeline and its decisions with Morris method. The visualizations provided will be for global explanations.

from interpret import set_visualize_provider
from interpret.provider import InlineProvider
set_visualize_provider(InlineProvider())

import numpy as np
from sklearn.datasets import load_breast_cancer
from sklearn.model_selection import train_test_split

from sklearn.ensemble import RandomForestClassifier
from sklearn.decomposition import PCA
from sklearn.pipeline import Pipeline

from interpret import show
from interpret.blackbox import MorrisSensitivity

seed = 42
np.random.seed(seed)
X, y = load_breast_cancer(return_X_y=True, as_frame=True)
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.20, random_state=seed)

pca = PCA()
rf = RandomForestClassifier(random_state=seed)

blackbox_model = Pipeline([('pca', pca), ('rf', rf)])
blackbox_model.fit(X_train, y_train)

msa = MorrisSensitivity(blackbox_model, X_train)

show(msa.explain_global())

Further Resources

• Wikipedia on Morris Method

Bibliography

[1] Max D Morris. Factorial sampling plans for preliminary computational experiments. Technometrics, 33(2):161–174, 1991.

[2] Jon Herman and Will Usher. Salib: an open-source python library for sensitivity analysis. Journal of Open Source Software, 2(9):97, 2017.