spreg.GM_Error_Hom¶

class spreg.GM_Error_Hom(y, x, w, slx_lags=0, slx_vars='All', max_iter=1, epsilon=1e-05, A1='hom_sc', vm=False, name_y=None, name_x=None, name_w=None, name_ds=None, latex=False, hard_bound=False)[source]¶

GMM method for a spatial error model with homoskedasticity, with results and diagnostics; based on Drukker et al. (2013) [DEP13], following Anselin (2011) [Ans11].

Parameters:

ynumpy.ndarray or pandas.Series: nx1 array for dependent variable
xnumpy.ndarray or pandas object: Two dimensional array with n rows and one column for each independent (exogenous) variable, excluding the constant
wpysal W object: Spatial weights object
slx_lagsinteger: Number of spatial lags of X to include in the model specification. If slx_lags>0, the specification becomes of the SLX-Error type.
slx_varseither “All” (default) or list of booleans to select x variables: to be lagged
max_iterint: Maximum number of iterations of steps 2a and 2b from [ADKP10]. Note: epsilon provides an additional stop condition.
epsilonfloat: Minimum change in lambda required to stop iterations of steps 2a and 2b from [ADKP10]. Note: max_iter provides an additional stop condition.
A1str: If A1=’het’, then the matrix A1 is defined as in Arraiz et al. If A1=’hom’, then as in [Ans11]. If A1=’hom_sc’ (default), then as in [DEP13] and [DPR13].
vmbool: If True, include variance-covariance matrix in summary results
name_ystr: Name of dependent variable for use in output
name_xlist of strings: Names of independent variables for use in output
name_wstr: Name of weights matrix for use in output
name_dsstr: Name of dataset for use in output
latexbool: Specifies if summary is to be printed in latex format
hard_boundbool: If true, raises an exception if the estimated spatial autoregressive parameter is outside the maximum/minimum bounds.
Attributes
———-
outputdataframe: regression results pandas dataframe
summarystr: Summary of regression results and diagnostics (note: use in conjunction with the print command)
betasarray: kx1 array of estimated coefficients
uarray: nx1 array of residuals
e_filteredarray: nx1 array of spatially filtered residuals
predyarray: nx1 array of predicted y values
ninteger: Number of observations
kinteger: Number of variables for which coefficients are estimated (including the constant)
yarray: nx1 array for dependent variable
xarray: Two dimensional array with n rows and one column for each independent (exogenous) variable, including the constant
iter_stopstr: Stop criterion reached during iteration of steps 2a and 2b from [ADKP10].
iterationinteger: Number of iterations of steps 2a and 2b from Arraiz et al.
mean_yfloat: Mean of dependent variable
std_yfloat: Standard deviation of dependent variable
pr2float: Pseudo R squared (squared correlation between y and ypred)
vmarray: Variance covariance matrix (kxk)
sig2float: Sigma squared used in computations
std_errarray: 1xk array of standard errors of the betas
z_statlist of tuples: z statistic; each tuple contains the pair (statistic, p-value), where each is a float
xtxfloat: \(X'X\)
name_ystr: Name of dependent variable for use in output
name_xlist of strings: Names of independent variables for use in output
name_wstr: Name of weights matrix for use in output
name_dsstr: Name of dataset for use in output
titlestr: Name of the regression method used

Examples

We first need to import the needed modules, namely numpy to convert the data we read into arrays that spreg understands and pysal to perform all the analysis.

>>> import numpy as np
>>> import libpysal

Open data on Columbus neighborhood crime (49 areas) using libpysal.io.open(). This is the DBF associated with the Columbus shapefile. Note that libpysal.io.open() also reads data in CSV format; since the actual class requires data to be passed in as numpy arrays, the user can read their data in using any method.

>>> db = libpysal.io.open(libpysal.examples.get_path('columbus.dbf'),'r')

Extract the HOVAL column (home values) from the DBF file and make it the dependent variable for the regression. Note that PySAL requires this to be an numpy array of shape (n, 1) as opposed to the also common shape of (n, ) that other packages accept.

>>> y = np.array(db.by_col("HOVAL"))
>>> y = np.reshape(y, (49,1))

Extract INC (income) and CRIME (crime) vectors from the DBF to be used as independent variables in the regression. Note that PySAL requires this to be an nxj numpy array, where j is the number of independent variables (not including a constant). By default this class adds a vector of ones to the independent variables passed in.

>>> X = []
>>> X.append(db.by_col("INC"))
>>> X.append(db.by_col("CRIME"))
>>> X = np.array(X).T

Since we want to run a spatial error model, we need to specify the spatial weights matrix that includes the spatial configuration of the observations into the error component of the model. To do that, we can open an already existing gal file or create a new one. In this case, we will create one from columbus.shp.

>>> w = libpysal.weights.Rook.from_shapefile(libpysal.examples.get_path("columbus.shp"))

Unless there is a good reason not to do it, the weights have to be row-standardized so every row of the matrix sums to one. Among other things, his allows to interpret the spatial lag of a variable as the average value of the neighboring observations. In PySAL, this can be easily performed in the following way:

>>> w.transform = 'r'

We are all set with the preliminars, we are good to run the model. In this case, we will need the variables and the weights matrix. If we want to have the names of the variables printed in the output summary, we will have to pass them in as well, although this is optional.

>>> reg = GM_Error_Hom(y, X, w=w, A1='hom_sc', name_y='home value', name_x=['income', 'crime'], name_ds='columbus')

Once we have run the model, we can explore a little bit the output. The regression object we have created has many attributes so take your time to discover them. This class offers an error model that assumes homoskedasticity but that unlike the models from spreg.error_sp, it allows for inference on the spatial parameter. This is why you obtain as many coefficient estimates as standard errors, which you calculate taking the square root of the diagonal of the variance-covariance matrix of the parameters:

>>> print(np.around(np.hstack((reg.betas,np.sqrt(reg.vm.diagonal()).reshape(4,1))),4))
[[47.9479 12.3021]
 [ 0.7063  0.4967]
 [-0.556   0.179 ]
 [ 0.4129  0.1835]]

__init__(y, x, w, slx_lags=0, slx_vars='All', max_iter=1, epsilon=1e-05, A1='hom_sc', vm=False, name_y=None, name_x=None, name_w=None, name_ds=None, latex=False, hard_bound=False)[source]¶

Methods

__init__(y, x, w[, slx_lags, slx_vars, ...])

Attributes

`mean_y`
`std_y`

property mean_y¶

property std_y¶