Customize Data Drift

All Metrics and Presets that evaluate shift in data distributions use the default Data Drift algorithm. It automatically selects the drift detection method based on the column type (text, categorical, numerical) and volume. You can override the defaults by passing a custom parameter to the chosen Metric or Preset. You can modify the drift detection method (choose from 20+ available), thresholds, or both. You can also implement fully custom drift detection methods. Pre-requisites:

You know how to use Data Definition to map column types.
You know how to create Reports and run Tests.

Data drift parameters

Setting conditions for data drift works differently from the usual Test API (with gt, lt, etc.) This accounts for nuances like varying role of thresholds across drift detection methods, where “greater” can be better or worse depending on the method.

Dataset-level

Dataset drift share. You can set the share of drifting columns that signals dataset drift (default: 0.5) in the relevant Metrics or Presets. For example, to set it at 70%:

report = Report([
    DataDriftPreset(drift_share=0.7)
]

This will detect dataset drift if over 70% columns are drifting, using defaults for each column. Drift methods. You can also specify the drift detection methods used on the column level. For example, to use PSI (Population Stability Index) for all columns in the dataset:

report = Report([
    DataDriftPreset(drift_share=0.7, method="psi")
]

This will check if over 70% columns are drifting, using PSI method with default thresholds.

See all available methods in the table below.

Drift thresholds. You can set thresholds for each method. For example, use PSI with a threshold of 0.3 for categorical columns.

report = Report([
    DataDriftPreset(cat_method="psi", cat_threshold="0.3")
]

In this case, if PSI is ≥ 0.3 for any categorical column, drift will be detected for that column. The rest of the checks will use defaults: default methods for numerical and text columns (if present), and 50% as the drift_share threshold.

Column-level

For column-level metrics, you can set the drift method/threshold directly for each column:

report = Report([
    ValueDrift(column="Salary", method="psi"),
]

All parameters

Use the following parameters to pass chosen drift methods. See methods and their defaults below.

Parameter	Description	Applies To
`method`	Defines the drift detection method for a given column (if one column is tested), or all columns in the dataset (if multiple columns are tested and the method can apply to all columns).	`ValueDrift()`, `DriftedColumnsCount()`, `DataDriftPreset()`
`threshold`	Sets the drift threshold in a given column or all columns. The threshold meaning varies based on the drift detection method, e.g., it can be the value of a distance metric or a p-value of a statistical test.	`ValueDrift()`, `DriftedColumnsCount()`, `DataDriftPreset()`
`drift_share`	Defines the share of drifting columns as a condition for Dataset Drift. Default: 0.5	`DriftedColumnsCount()`, `DataDriftPreset()`
`cat_method` `cat_threshold`	Sets the drift method and/or threshold for all categorical columns.	`DriftedColumnsCount()`, `DataDriftPreset()`
`num_method` `num_threshold`	Sets the drift method and/or threshold for all numerical columns.	`DriftedColumnsCount()`, `DataDriftPreset()`
`per_column_method` `per_column_threshold`	Sets the drift method and/or threshold for the listed columns (accepts a dictionary).	`DriftedColumnsCount()`, `DataDriftPreset()`
`text_method` `text_threshold`	Defines the drift detection method and threshold for all text columns.	`DriftedColumnsCount()`, `DataDriftPreset()`

Data drift detection methods

Tabular data

The following methods apply to tabular data: numerical or categorical columns in data definition. Pass them using the stattest (or num_stattest, etc.) parameter.

StatTest	Applicable to	Drift score
`ks` Kolmogorov–Smirnov (K-S) test	tabular data only numerical Default method for numerical data, if ≤ 1000 objects	returns `p_value` drift detected when `p_value < threshold` default threshold: 0.05
`chisquare` Chi-Square test	tabular data only categorical Default method for categorical with > 2 labels, if ≤ 1000 objects	returns `p_value` drift detected when `p_value < threshold` default threshold: 0.05
`z` Z-test	tabular data only categorical Default method for binary data, if ≤ 1000 objects	returns `p_value` drift detected when `p_value < threshold` default threshold: 0.05
`wasserstein` Wasserstein distance (normed)	tabular data only numerical Default method for numerical data, if > 1000 objects	returns `distance` drift detected when `distance` ≥ `threshold` default threshold: 0.1
`kl_div` Kullback-Leibler divergence	tabular data numerical and categorical	returns `divergence` drift detected when `divergence` ≥ `threshold` default threshold: 0.1
`psi` Population Stability Index (PSI)	tabular data numerical and categorical	returns `psi_value` drift detected when `psi_value` ≥ `threshold` default threshold: 0.1
`jensenshannon` Jensen-Shannon distance	tabular data numerical and categorical Default method for categorical, if > 1000 objects	returns `distance` drift detected when `distance` ≥ `threshold` default threshold: 0.1
`anderson` Anderson-Darling test	tabular data only numerical	returns `p_value` drift detected when `p_value < threshold` default threshold: 0.05
`fisher_exact` Fisher’s Exact test	tabular data only categorical	returns `p_value` drift detected when `p_value < threshold` default threshold: 0.05
`cramer_von_mises` Cramer-Von-Mises test	tabular data only numerical	returns `p_value` drift detected when `p_value < threshold` default threshold: 0.05
`g-test` G-test	tabular data only categorical	returns `p_value` drift detected when `p_value < threshold` default threshold: 0.05
`hellinger` Hellinger Distance (normed)	tabular data numerical and categorical	returns `distance` drift detected when `distance` >= `threshold` default threshold: 0.1
`mannw` Mann-Whitney U-rank test	tabular data only numerical	returns `p_value` drift detected when `p_value < threshold` default threshold: 0.05
`ed` Energy distance	tabular data only numerical	returns `distance` drift detected when `distance >= threshold` default threshold: 0.1
`es` Epps-Singleton test	tabular data only numerical	returns `p_value` drift detected when `p_value < threshold` default threshold: 0.05
`t_test` T-Test	tabular data only numerical	returns `p_value` drift detected when `p_value < threshold` default threshold: 0.05
`empirical_mmd` Empirical-MMD	tabular data only numerical	returns `p_value` drift detected when `p_value < threshold` default threshold: 0.05
`TVD` Total-Variation-Distance	tabular data only categorical	returns `p_value` drift detected when `p_value` < `threshold` default threshold: 0.05

Text data

Text drift detection applies to columns with raw text data, as specified in data definition. Pass them using the stattest (or text_stattest) parameter.

StatTest	Description	Drift score
`perc_text_content_drift` Text content drift (domain classifier, with statistical hypothesis testing)	Applies only to text data. Trains a classifier model to distinguish between text in “current” and “reference” datasets. Default for text data ≤ 1000 objects.	returns `roc_auc` of the classifier as a `drift_score` drift detected when `roc_auc` > possible ROC AUC of the random classifier at a set percentile `threshold` sets the percentile of the possible ROC AUC values of the random classifier to compare against default threshold: 0.95 (95th percentile) `roc_auc` values can be 0 to 1 (typically 0.5 to 1); a higher value means more confident drift detection
`abs_text_content_drift` Text content drift (domain classifier)	Applies only to text data. Trains a classifier model to distinguish between text in “current” and “reference” datasets. Default for text data when > 1000 objects.	returns `roc_auc` of the classifier as a `drift_score` drift detected when `roc_auc` > `threshold` `threshold` sets the ROC AUC threshold default threshold: 0.55 `roc_auc` values can be 0 to 1 (typically 0.5 to 1); a higher value means more confident drift detection

Text descriptors drift. If you work with raw text data, you can also check for distribution drift in text descriptors (such as text length, etc.) To use this method, first compute the selected text descriptors. Then, use numerical / categorical drift detection methods as usual.

Add a custom method

If you do not find a suitable drift detection method, you can implement a custom function:

import pandas as pd
from scipy.stats import anderson_ksamp

from evidently import Dataset
from evidently import DataDefinition
from evidently import Report
from evidently import ColumnType
from evidently.metrics import ValueDrift
from evidently.metrics import DriftedColumnsCount
from evidently.legacy.calculations.stattests import register_stattest
from evidently.legacy.calculations.stattests import StatTest

#toy data 
data = pd.DataFrame(data={
    "column_1": [1, 2, 3, 4, -1, 5],
    "target": [1, 1, 0, 0, 1, 1],
    "prediction": [0.1, 0.2, 0.3, 0.4, 0.5, 0.6],
})

definition = DataDefinition(
    numerical_columns=["column_1", "target", "prediction"],
    )
dataset = Dataset.from_pandas(
    data,
    data_definition=definition,
)

#implement method
def _addd(
    reference_data: pd.Series,
    current_data: pd.Series,
    feature_type: ColumnType,
    threshold: float,
):
    p_value = anderson_ksamp([reference_data.values, current_data.values])[2]
    return p_value, p_value < threshold


adt = StatTest(
    name="adt",
    display_name="Anderson-Darling",
    allowed_feature_types=[ColumnType.Numerical],
    default_threshold=0.1,
)

register_stattest(adt, default_impl=_addd)


report = Report([
    # ValueDrift(column="column_1"),
    ValueDrift(column="column_1", method="adt"),
    DriftedColumnsCount(),
])

snapshot = report.run(dataset, dataset)
snapshot

We recommended writing a specific instance of the StatTest class for that function. You need:

Parameter	Type	Description
`name`	`str`	A short name used to reference the Stat Test from the options (registered globally).
`display_name`	`str`	A long name displayed in the Report.
`func`	`Callable`	The StatTest function.
`allowed_feature_types`	`List[str]`	The list of allowed feature types for this function (`cat`, `num`).

The StatTest function itself should match (reference_data: pd.Series, current_data: pd.Series, threshold: float) -> Tuple[float, bool] signature. Accepts:

reference_data: pd.Series - The reference data series.
current_data: pd.Series - The current data series to compare.
feature_type: str - The type of feature being analyzed.
threshold: float - The test threshold for drift detection.

Returns:

score: float - Stat Test score (actual value)
drift_detected: bool - indicates is drift detected with given threshold

Reference

Metric Customization

Explainers

Data drift parameters

Dataset-level

Column-level

All parameters

Data drift detection methods

Tabular data

Text data

Add a custom method

​Data drift parameters

​Dataset-level

​Column-level

​All parameters

​Data drift detection methods

​Tabular data

​Text data

​Add a custom method

Data drift parameters

Dataset-level

Column-level

All parameters

Data drift detection methods

Tabular data

Text data

Add a custom method