Model Testing

pgmpy.metrics.correlation_score(model, data, test='chi_square', significance_level=0.05, score=<function f1_score>, return_summary=False)

Function to score how well the model structure represents the correlations in the data. The model doesn’t need to be parameterized for this score.

A Bayesian Network or DAG has d-connection property which can be used to determine which variables are correlated according to the model. This function uses this d-connection/d-separation property to compare the model with variable correlations in a given dataset. For every pair of variables in the dataset, a correlation test (specified by test argument) is done. We say that any two variables are correlated if the test’s p-value < significance_level. The same pair of variables are then tested whether they are d-connected in the network structure or not. Finally, a metric specified by score is computed by using the correlation test as the true value and d-connections as predicted values.

Absense of correlation/d-separation is considered as the positive class for computing the metrics.

Parameters:

• model (Instance of pgmpy.base.DAG or pgmpy.models.BayesianNetwork) – The model which needs to be tested.

• data (pandas.DataFrame instance) – The dataset against which to test the model structure.

• test (str or function) – The statistical tests to use for determining whether the variables in data are correlated or not. For discrete variables, the options are: 1) chi_square 2) g_sq 3) log_likelihood 4) freeman_tuckey 5) modified_log_likelihood 6) neyman 7) cressie_read. For continuous variables only one test is available: 1) pearsonr. A function with the signature fun(X, Y, Z, data) can also be passed which returns True for uncorrelated and False otherwise.

• significance_level (float) – A value between 0 and 1. If p_value < significance_level, the variables are considered uncorrelated.

• score (function (default: f1-score)) – Any classification scoring metric from scikit-learn. https://scikit-learn.org/stable/modules/classes.html#classification-metrics

• return_summary (boolean (default: False)) – If True, returns a dataframe with details for each of the conditions checked.

Returns:

The specified metric – The metric specified by the score argument. By defults returns the f1-score.

Return type:

float

Examples

>>> from pgmpy.utils import get_examples_model
>>> from pgmpy.metrics import correlation_score
>>> alarm = get_example_model("alarm")
>>> data = alarm.simulate(int(1e4))
>>> correlation_score(alarm, data, test="chi_square", significance_level=0.05)
0.911957950065703

pgmpy.metrics.log_likelihood_score(model, data)

Computes the log-likelihood of a given dataset i.e. P(data | model).

The log-likelihood measure can be used to check how well the specified model describes the data. This method requires the parameters of the model to be specified as well. Direct interpretation of this score is difficult but can be used to compare the fit of two or more models. A higher score means ab better fit.

Parameters:

• model (pgmpy.base.DAG or pgmpy.models.BayesianNetwork instance) – The model whose score needs to be computed.

• data (pd.DataFrame instance) – The dataset against which to score the model.

Examples

>>> from pgmpy.metrics import log_likelihood_score
>>> from pgmpy.utils import get_example_model
>>> model = get_example_model("alarm")
>>> data = model.simulate(int(1e4))
>>> log_likelihood_score(model, data)
-103818.57516969478

pgmpy.metrics.structure_score(model, data, scoring_method='bic', **kwargs)

Uses the standard model scoring methods to give a score for each structure. The score doesn’t have very straight forward interpretebility but can be used to compare different models. A higher score represents a better fit. This method only needs the model structure to compute the score and parameters aren’t required.

Parameters:

• model (pgmpy.base.DAG or pgmpy.models.BayesianNetwork instance) – The model whose score needs to be computed.

• data (pd.DataFrame instance) – The dataset against which to score the model.

• scoring_method (str ( k2 | bdeu | bds | bic )) – The following four scoring methods are supported currently: 1) K2Score 2) BDeuScore 3) BDsScore 4) BicScore

• kwargs (kwargs) – Any additional parameters that needs to be passed to the scoring method. Check pgmpy.estimators.StructureScore for details.

Returns:

Model score – A score value for the model.

Return type:

float

Examples

>>> from pgmpy.utils import get_example_model
>>> from pgmpy.metrics import structure_score
>>> model = get_example_model('alarm')
>>> data = model.simulate(int(1e4))
>>> structure_score(model, data, scoring_method="bic")
-106665.9383064447

class pgmpy.metrics.bn_inference.BayesianModelProbability(model)

Class to calculate probability (pmf) values specific to Bayesian Models

log_probability(data, ordering=None)

Evaluate the logarithmic probability of each point in a data set.

Parameters:

• data (pandas dataframe OR array_like, shape (n_samples, n_features)) – List of n_features-dimensional data points. Each row corresponds to a single data point.

• ordering (list) – ordering of columns in data, used by the Bayesian model. default is topological ordering used by model.

Returns:

Log probability of each datapoint – The array of log(density) evaluations. These are normalized to be probability densities, so values will be low for high-dimensional data.

Return type:

np.array (n_samples,)

score(data, ordering=None)

Compute the total log probability density under the model.

Parameters:

• data (pandas dataframe OR array_like, shape (n_samples, n_features)) – List of n_features-dimensional data points. Each row corresponds to a single data point.

• ordering (list) – ordering of columns in data, used by the Bayesian model. default is topological ordering used by model.

Returns:

Log-likelihood of data – This is normalized to be a probability density, so the value will be low for high-dimensional data.

Return type:

float