Out-of-sample validation

Example of the out-of-sample validation of a logit model.

author:

Michel Bierlaire, EPFL

date:

Sun Apr 9 17:24:32 2023

import biogeme.biogeme as bio
from biogeme import models
from biogeme.expressions import Beta

See the data processing script: Data preparation for Swissmetro.

from swissmetro_data import (
    database,
    CHOICE,
    SM_AV,
    CAR_AV_SP,
    TRAIN_AV_SP,
    TRAIN_TT_SCALED,
    TRAIN_COST_SCALED,
    SM_TT_SCALED,
    SM_COST_SCALED,
    CAR_TT_SCALED,
    CAR_CO_SCALED,
)

Parameters to be estimated.

ASC_CAR = Beta('ASC_CAR', 0, None, None, 0)
ASC_TRAIN = Beta('ASC_TRAIN', 0, None, None, 0)
ASC_SM = Beta('ASC_SM', 0, None, None, 1)
B_TIME = Beta('B_TIME', 0, None, None, 0)
B_COST = Beta('B_COST', 0, None, None, 0)

Definition of the utility functions.

V1 = ASC_TRAIN + B_TIME * TRAIN_TT_SCALED + B_COST * TRAIN_COST_SCALED
V2 = ASC_SM + B_TIME * SM_TT_SCALED + B_COST * SM_COST_SCALED
V3 = ASC_CAR + B_TIME * CAR_TT_SCALED + B_COST * CAR_CO_SCALED

Associate utility functions with the numbering of alternatives.

V = {1: V1, 2: V2, 3: V3}

Associate the availability conditions with the alternatives.

av = {1: TRAIN_AV_SP, 2: SM_AV, 3: CAR_AV_SP}

Definition of the model. This is the contribution of each observation to the log likelihood function.

logprob = models.loglogit(V, av, CHOICE)

Create the Biogeme object.

the_biogeme = bio.BIOGEME(database, logprob)
the_biogeme.modelName = 'b04validation'

Estimate the parameters.

results = the_biogeme.estimate()

The validation consists in organizing the data into several slices of about the same size, randomly defined. Each slice is considered as a validation dataset. The model is then re-estimated using all the data except the slice, and the estimated model is applied on the validation set (i.e. the slice). The value of the log likelihood for each observation in the validation set is reported in a dataframe. As this is done for each slice, the output is a list of dataframes, each corresponding to one of these exercises.

validation_data = database.split(slices=5)

validation_results = the_biogeme.validate(results, validation_data)

for slide in validation_results:
    print(
        f'Log likelihood for {slide.shape[0]} validation data: '
        f'{slide["Loglikelihood"].sum()}'
    )

/Users/bierlair/venv312/lib/python3.12/site-packages/numpy/_core/fromnumeric.py:57: FutureWarning: 'DataFrame.swapaxes' is deprecated and will be removed in a future version. Please use 'DataFrame.transpose' instead.
  return bound(*args, **kwds)
Log likelihood for 1354 validation data: -1072.160299473448
Log likelihood for 1354 validation data: -1040.1429748703445
Log likelihood for 1354 validation data: -1023.5165744383794
Log likelihood for 1353 validation data: -1123.2285680838186
Log likelihood for 1353 validation data: -1085.448634513827