Source code for statsmodels.multivariate.factor

# -*- coding: utf-8 -*-

from __future__ import division
from statsmodels.base.model import Model
from .factor_rotation import rotate_factors, promax
import numpy as np
from numpy.linalg import eigh, inv, norm, matrix_rank
import pandas as pd
from import cache_readonly
from scipy.optimize import minimize
from statsmodels.iolib import summary2
import warnings

    import matplotlib.pyplot
    missing_matplotlib = False
except ImportError:
    missing_matplotlib = True

if not missing_matplotlib:
    from .plots import plot_scree, plot_loadings

_opt_defaults = {'gtol': 1e-7}

def _check_args_1(endog, n_factor, corr, nobs):

    msg = "Either endog or corr must be provided."
    if endog is not None and corr is not None:
        raise ValueError(msg)
    if endog is None and corr is None:
        warnings.warn('Both endog and corr are provided, ' +
                      'corr will be used for factor analysis.')

    if n_factor <= 0:
        raise ValueError('n_factor must be larger than 0! %d < 0' %

    if nobs is not None and endog is not None:
        warnings.warn("nobs is ignored when endog is provided")

def _check_args_2(endog, n_factor, corr, nobs, k_endog):

    if n_factor > k_endog:
        raise ValueError('n_factor cannot be greater than the number'
                         ' of variables! %d > %d' %
                         (n_factor, k_endog))

    if np.max(np.abs(np.diag(corr) - 1)) > 1e-10:
        raise ValueError("corr must be a correlation matrix")

    if corr.shape[0] != corr.shape[1]:
        raise ValueError('Correlation matrix corr must be a square '
                         '(rows %d != cols %d)' % corr.shape)

[docs]class Factor(Model): """ Factor analysis Parameters ---------- endog : array-like Variables in columns, observations in rows. May be `None` if `corr` is not `None`. n_factor : int The number of factors to extract corr : array-like Directly specify the correlation matrix instead of estimating it from `endog`. If provided, `endog` is not used for the factor analysis, it may be used in post-estimation. method : str The method to extract factors, currently must be either 'pa' for principal axis factor analysis or 'ml' for maximum likelihood estimation. smc : True or False Whether or not to apply squared multiple correlations (method='pa') endog_names: str Names of endogeous variables. If specified, it will be used instead of the column names in endog nobs : int The number of observations, not used if endog is present. Needs to be provided for inference if endog is None. missing : 'none', 'drop', or 'raise' Missing value handling for endog, default is row-wise deletion 'drop' If 'none', no nan checking is done. If 'drop', any observations with nans are dropped. If 'raise', an error is raised. Notes ----- **Experimental** Supported rotations: 'varimax', 'quartimax', 'biquartimax', 'equamax', 'oblimin', 'parsimax', 'parsimony', 'biquartimin', 'promax' If method='ml', the factors are rotated to satisfy condition IC3 of Bai and Li (2012). This means that the scores have covariance I, so the model for the covariance matrix is L * L' + diag(U), where L are the loadings and U are the uniquenesses. In addition, L' * diag(U)^{-1} L must be diagonal. References ---------- .. [*] Hofacker, C. (2004). Exploratory Factor Analysis, Mathematical Marketing. .. [*] J Bai, K Li (2012). Statistical analysis of factor models of high dimension. Annals of Statistics. """ def __init__(self, endog=None, n_factor=1, corr=None, method='pa', smc=True, endog_names=None, nobs=None, missing='drop'): _check_args_1(endog, n_factor, corr, nobs) if endog is not None: super(Factor, self).__init__(endog, exog=None, missing=missing) endog = self.endog # after preprocessing like missing, asarray k_endog = endog.shape[1] nobs = endog.shape[0] corr = self.corr = np.corrcoef(endog, rowvar=0) elif corr is not None: corr = self.corr = np.asarray(corr) k_endog = self.corr.shape[0] self.endog = None else: msg = "Either endog or corr must be provided." raise ValueError(msg) _check_args_2(endog, n_factor, corr, nobs, k_endog) self.n_factor = n_factor self.loadings = None self.communality = None self.method = method self.smc = smc self.nobs = nobs self.method = method self.corr = corr self.k_endog = k_endog if endog_names is None: if hasattr(corr, 'index'): endog_names = corr.index if hasattr(corr, 'columns'): endog_names = corr.columns self.endog_names = endog_names @property def endog_names(self): """Names of endogenous variables""" if self._endog_names is not None: return self._endog_names else: if self.endog is not None: return else: d = 0 n = self.corr.shape[0] - 1 while n > 0: d += 1 n //= 10 return [('var%0' + str(d) + 'd') % i for i in range(self.corr.shape[0])] @endog_names.setter def endog_names(self, value): # Check validity of endog_names: if value is not None: if len(value) != self.corr.shape[0]: raise ValueError('The length of `endog_names` must ' 'equal the number of variables.') self._endog_names = np.asarray(value) else: self._endog_names = None
[docs] def fit(self, maxiter=50, tol=1e-8, start=None, opt_method='BFGS', opt=None, em_iter=3): """ Estimate factor model parameters. Parameters ---------- maxiter : int Maximum number of iterations for iterative estimation algorithms tol : float Stopping critera (error tolerance) for iterative estimation algorithms start : array-like Starting values, currently only used for ML estimation opt_method : string Optimization method for ML estimation opt : dict-like Keyword arguments passed to optimizer, only used for ML estimation em_iter : int The number of EM iterations before starting gradient optimization, only used for ML estimation. Returns ------- results: FactorResults """ method = self.method.lower() if method == 'pa': return self._fit_pa(maxiter=maxiter, tol=tol) elif method == 'ml': return self._fit_ml(start, em_iter, opt_method, opt) else: msg = "Unknown factor extraction approach '%s'" % self.method raise ValueError(msg)
def _fit_pa(self, maxiter=50, tol=1e-8): """ Extract factors using the iterative principal axis method Parameters ---------- maxiter : int Maximum number of iterations for communality estimation tol : float If `norm(communality - last_communality) < tolerance`, estimation stops Returns ------- results : FactorResults instance """ R = self.corr.copy() # inplace modification below # Parameter validation self.n_comp = matrix_rank(R) if self.n_factor > self.n_comp: raise ValueError('n_factor must be smaller or equal to the rank' ' of endog! %d > %d' % (self.n_factor, self.n_comp)) if maxiter <= 0: raise ValueError('n_max_iter must be larger than 0! %d < 0' % (maxiter)) if tol <= 0 or tol > 0.01: raise ValueError('tolerance must be larger than 0 and smaller than' ' 0.01! Got %f instead' % (tol)) # Initial communality estimation if self.smc: c = 1 - 1 / np.diag(inv(R)) else: c = np.ones(len(R)) # Iterative communality estimation eigenvals = None for i in range(maxiter): # Get eigenvalues/eigenvectors of R with diag replaced by # communality for j in range(len(R)): R[j, j] = c[j] L, V = eigh(R, UPLO='U') c_last = np.array(c) ind = np.argsort(L) ind = ind[::-1] L = L[ind] n_pos = (L > 0).sum() V = V[:, ind] eigenvals = np.array(L) # Select eigenvectors with positive eigenvalues n = np.min([n_pos, self.n_factor]) sL = np.diag(np.sqrt(L[:n])) V = V[:, :n] # Calculate new loadings and communality A = c = np.power(A, 2).sum(axis=1) if norm(c_last - c) < tol: break self.eigenvals = eigenvals self.communality = c self.uniqueness = 1 - c self.loadings = A return FactorResults(self) # Unpacks the model parameters from a flat vector, used for ML # estimation. The first k_endog elements of par are the square # roots of the uniquenesses. The remaining elements are the # factor loadings, packed one factor at a time. def _unpack(self, par): return (par[0:self.k_endog]**2, np.reshape(par[self.k_endog:], (-1, self.k_endog)).T) # Packs the model parameters into a flat parameter, used for ML # estimation. def _pack(self, load, uniq): return np.concatenate((np.sqrt(uniq), load.T.flat))
[docs] def loglike(self, par): """ Evaluate the log-likelihood function. Parameters ---------- par : ndarray or tuple of 2 ndarray's The model parameters, either a packed representation of the model parameters or a 2-tuple containing a `k_endog x n_factor` matrix of factor loadings and a `k_endog` vector of uniquenesses. Returns ------- loglike : float """ if type(par) is np.ndarray: uniq, load = self._unpack(par) else: load, uniq = par[0], par[1] loadu = load / uniq[:, None] lul =, loadu) # log|GG' + S| # Using matrix determinant lemma: # |GG' + S| = |I + G'S^{-1}G|*|S| lul.flat[::lul.shape[0]+1] += 1 _, ld = np.linalg.slogdet(lul) v = np.sum(np.log(uniq)) + ld # tr((GG' + S)^{-1}C) # Using Sherman-Morrison-Woodbury w = np.sum(1 / uniq) b =, self.corr / uniq[:, None]) b = np.linalg.solve(lul, b) b =, b) w -= np.trace(b) # Scaled log-likelihood return -(v + w) / (2*self.k_endog)
[docs] def score(self, par): """ Evaluate the score function (first derivative of loglike). Parameters ---------- par : ndarray or tuple of 2 ndarray's The model parameters, either a packed representation of the model parameters or a 2-tuple containing a `k_endog x n_factor` matrix of factor loadings and a `k_endog` vector of uniquenesses. Returns ------- score : ndarray """ if type(par) is np.ndarray: uniq, load = self._unpack(par) else: load, uniq = par[0], par[1] # Center term of SMW loadu = load / uniq[:, None] c =, loadu) c.flat[::c.shape[0]+1] += 1 d = np.linalg.solve(c, load.T) # Precompute these terms lud =, d) cu = (self.corr / uniq) / uniq[:, None] r =, load) lul =, load) luz =, lul) # First term du = 2*np.sqrt(uniq) * (1/uniq - (d * load.T).sum(0) / uniq**2) dl = 2*(loadu -, loadu)) # Second term h =, cu) f =, lud.T) du -= 2*np.sqrt(uniq) * (np.diag(cu) - 2*np.diag(h) + np.diag(f)) dl -= 2*r dl += 2*, r) dl += 2*luz dl -= 2*, luz) # Can't use _pack because we are working with the square root # uniquenesses directly. return -np.concatenate((du, dl.T.flat)) / (2*self.k_endog)
# Maximum likelihood factor analysis. def _fit_ml(self, start, em_iter, opt_method, opt): """estimate Factor model using Maximum Likelihood """ # Starting values if start is None: load, uniq = self._fit_ml_em(em_iter) start = self._pack(load, uniq) elif len(start) == 2: if len(start[1]) != start[0].shape[0]: msg = "Starting values have incompatible dimensions" raise ValueError(msg) start = self._pack(start[0], start[1]) else: raise ValueError("Invalid starting values") def nloglike(par): return -self.loglike(par) def nscore(par): return -self.score(par) # Do the optimization if opt is None: opt = _opt_defaults r = minimize(nloglike, start, jac=nscore, method=opt_method, options=opt) if not r.success: warnings.warn("Fitting did not converge") par = r.x uniq, load = self._unpack(par) if uniq.min() < 1e-10: warnings.warn("Some uniquenesses are nearly zero") # Rotate solution to satisfy IC3 of Bai and Li load = self._rotate(load, uniq) self.uniqueness = uniq self.communality = 1 - uniq self.loadings = load self.mle_retvals = r return FactorResults(self) def _fit_ml_em(self, iter): """estimate Factor model using EM algorithm """ # Starting values np.random.seed(3427) load = 0.1*np.random.normal(size=(self.k_endog, self.n_factor)) uniq = 0.5 * np.ones(self.k_endog) for k in range(iter): loadu = load / uniq[:, None] f =, loadu) f.flat[::f.shape[0]+1] += 1 r = np.linalg.solve(f, loadu.T) q =, load) h =, load) c = load -, h) c /= uniq[:, None] g =, r) e =, self.corr) d =, self.corr) - e a =, c) a -=, c) a.flat[::a.shape[0]+1] += 1 b =, c) load = np.linalg.solve(a, b.T).T uniq = np.diag(self.corr) - (load * d.T).sum(1) return load, uniq def _rotate(self, load, uniq): """rotate loadings for MLE """ # Rotations used in ML estimation. load, s, _ = np.linalg.svd(load, 0) load *= s if self.nobs is None: nobs = 1 else: nobs = self.nobs cm =, load / uniq[:, None]) / nobs _, f = np.linalg.eig(cm) load =, f) return load
[docs]class FactorResults(object): """ Factor results class For result summary, scree/loading plots and factor rotations Parameters ---------- factor : Factor Fitted Factor class Attributes ---------- uniqueness: ndarray The uniqueness (variance of uncorrelated errors unique to each variable) communality: ndarray 1 - uniqueness loadings : ndarray Each column is the loading vector for one factor loadings_no_rot : ndarray Unrotated loadings, not available under maximum likelihood analyis. eigenvalues : ndarray The eigenvalues for a factor analysis obtained using principal components; not available under ML estimation. n_comp : int Number of components (factors) nbs : int Number of observations fa_method : string The method used to obtain the decomposition, either 'pa' for 'principal axes' or 'ml' for maximum likelihood. df : int Degrees of freedom of the factor model. Notes ----- Under ML estimation, the default rotation (used for `loadings`) is condition IC3 of Bai and Li (2012). Under this rotation, the factor scores are iid and standardized. If `G` is the canonical loadings and `U` is the vector of uniquenesses, then the covariance matrix implied by the factor analysis is `GG' + diag(U)`. Status: experimental, Some refactoring will be necessary when new features are added. """ def __init__(self, factor): self.model = factor self.endog_names = factor.endog_names self.loadings_no_rot = factor.loadings if hasattr(factor, "eigenvals"): self.eigenvals = factor.eigenvals self.communality = factor.communality self.uniqueness = factor.uniqueness self.rotation_method = None self.fa_method = factor.method self.n_comp = factor.loadings.shape[1] self.nobs = factor.nobs self._factor = factor if hasattr(factor, "mle_retvals"): self.mle_retvals = factor.mle_retvals p, k = self.loadings_no_rot.shape self.df = ((p - k)**2 - (p + k)) // 2 # no rotation, overwritten in `rotate` self.loadings = factor.loadings self.rotation_matrix = np.eye(self.n_comp) def __str__(self): return self.summary().__str__()
[docs] def rotate(self, method): """ Apply rotation, inplace modification of this Results instance Parameters ---------- method : string Rotation to be applied. Allowed methods are varimax, quartimax, biquartimax, equamax, oblimin, parsimax, parsimony, biquartimin, promax. Returns ------- None : nothing returned, modifications are inplace Notes ----- Warning: 'varimax', 'quartimax' and 'oblimin' are verified against R or Stata. Some rotation methods such as promax do not produce the same results as the R or Stata default functions. See Also -------- factor_rotation : subpackage that implements rotation methods """ self.rotation_method = method if method not in ['varimax', 'quartimax', 'biquartimax', 'equamax', 'oblimin', 'parsimax', 'parsimony', 'biquartimin', 'promax']: raise ValueError('Unknown rotation method %s' % (method)) if method in ['varimax', 'quartimax', 'biquartimax', 'equamax', 'parsimax', 'parsimony', 'biquartimin']: self.loadings, T = rotate_factors(self.loadings_no_rot, method) elif method == 'oblimin': self.loadings, T = rotate_factors(self.loadings_no_rot, 'quartimin') elif method == 'promax': self.loadings, T = promax(self.loadings_no_rot) else: raise ValueError('rotation method not recognized') self.rotation_matrix = T
def _corr_factors(self): """correlation of factors implied by rotation If the rotation is oblique, then the factors are correlated. currently not cached Returns ------- corr_f : ndarray correlation matrix of rotated factors, assuming initial factors are orthogonal """ T = self.rotation_matrix corr_f = return corr_f
[docs] def factor_score_params(self, method='bartlett'): """compute factor scoring coefficient matrix The coefficient matrix is not cached. Parameters ---------- method : 'bartlett' or 'regression' Method to use for factor scoring. 'regression' can be abbreviated to `reg` Returns ------- coeff_matrix : ndarray matrix s to compute factors f from a standardized endog ys. ``f = ys dot s`` Notes ----- The `regression` method follows the Stata definition. Method bartlett and regression are verified against Stats. Two inofficial methods, 'ols' and 'gls', produce similar factor scores but are not verified. See Also -------- `factor_scoring` : compute factor scores using scoring matrix """ L = self.loadings T = self.rotation_matrix.T #TODO: check row versus column convention for T uni = 1 - self.communality #self.uniqueness if method == 'bartlett': s_mat = np.linalg.inv([:,None]))).dot((L.T / uni)).T elif method.startswith('reg'): corr = self.model.corr corr_f = self._corr_factors() # if orthogonal then corr_f is just eye s_mat = elif method == 'ols': # not verified corr = self.model.corr corr_f = self._corr_factors() s_mat = elif method == 'gls': # not verified #s_mat = np.linalg.inv(1*np.eye(L.shape[1]) +[:,None]))) corr = self.model.corr corr_f = self._corr_factors() s_mat = np.linalg.inv(np.linalg.inv(corr_f) +[:,None]))) s_mat = / uni).T else: raise ValueError('method not available, use "bartlett ' + 'or "regression"') return s_mat
[docs] def factor_scoring(self, endog=None, method='bartlett', transform=True): """factor scoring: compute factors for endog If endog was not provided when creating the factor class, then a standarized endog needs to be provided here. Parameters ---------- method : 'bartlett' or 'regression' Method to use for factor scoring. 'regression' can be abbreviated to `reg` transform : bool If transform is true and endog is provided, then it will be standardized using mean and scale of original data, which has to be available in this case. If transform is False, then a provided endog will be used unchanged. The original endog in the Factor class will always be standardized if endog is None, independently of `transform`. Returns ------- factor_score : ndarray estimated factors using scoring matrix s and standarized endog ys ``f = ys dot s`` Notes ----- Status: transform option is experimental and might change. See Also -------- `factor_score_params` : scoring matrix """ if transform is False and endog is not None: # no transformation in this case endog = np.asarray(endog) else: # we need to standardize with the original mean and scale if self.model.endog is not None: m = self.model.endog.mean(0) s = self.model.endog.std(ddof=1, axis=0) if endog is None: endog = self.model.endog else: endog = np.asarray(endog) else: raise ValueError('If transform is True, then `endog` needs ' + 'to be available in the Factor instance.') endog = (endog - m) / s s_mat = self.factor_score_params(method=method) factors = return factors
[docs] def summary(self): summ = summary2.Summary() summ.add_title('Factor analysis results') loadings_no_rot = pd.DataFrame( self.loadings_no_rot, columns=["factor %d" % (i) for i in range(self.loadings_no_rot.shape[1])], index=self.endog_names ) if hasattr(self, "eigenvals"): # eigenvals not available for ML method eigenvals = pd.DataFrame( [self.eigenvals], columns=self.endog_names, index=['']) summ.add_dict({'': 'Eigenvalues'}) summ.add_df(eigenvals) communality = pd.DataFrame([self.communality], columns=self.endog_names, index=['']) summ.add_dict({'': ''}) summ.add_dict({'': 'Communality'}) summ.add_df(communality) summ.add_dict({'': ''}) summ.add_dict({'': 'Pre-rotated loadings'}) summ.add_df(loadings_no_rot) summ.add_dict({'': ''}) if self.rotation_method is not None: loadings = pd.DataFrame( self.loadings, columns=["factor %d" % (i) for i in range(self.loadings.shape[1])], index=self.endog_names ) summ.add_dict({'': '%s rotated loadings' % (self.rotation_method)}) summ.add_df(loadings) return summ
[docs] def get_loadings_frame(self, style='display', sort_=True, threshold=0.3, highlight_max=True, color_max='yellow', decimals=None): """get loadings matrix as DataFrame or pandas Styler Parameters ---------- style : 'display' (default), 'raw' or 'strings' Style to use for display * 'raw' returns just a DataFrame of the loadings matrix, no options are applied * 'display' add sorting and styling as defined by other keywords * 'strings' returns a DataFrame with string elements with optional sorting and surpressing small loading coefficients. sort_ : boolean If True, then the rows of the DataFrame is sorted by contribution of each factor. applies if style is either 'display' or 'strings' threshold : float If the threshold is larger than zero, then loading coefficients are either colored white (if style is 'display') or replace by empty string (if style is 'strings'). highlight_max : boolean This add a background color to the largest coefficient in each row. color_max : html color default is 'yellow'. color for background of row maximum decimals : None or int If None, then pandas default precision applies. Otherwise values are rounded to the specified decimals. If style is 'display', then the underlying dataframe is not changed. If style is 'strings', then values are rounded before conversion to strings. Returns ------- loadings : DataFrame or pandas Styler instance The return is a pandas Styler instance, if style is 'display' and at least one of highlight_max, threshold or decimals is applied. Otherwise, the returned loadings is a DataFrame. Examples -------- >>> mod = Factor(df, 3, smc=True) >>> res = >>> res.get_loadings_frame(style='display', decimals=3, threshold=0.2) To get a sorted DataFrame, all styling options need to be turned off: >>> df_sorted = res.get_loadings_frame(style='display', ... highlight_max=False, decimals=None, threshold=0) Options except for highlighting are available for plain test or Latex usage: >>> lds = res_u.get_loadings_frame(style='strings', decimals=3, ... threshold=0.3) >>> print(lds.to_latex()) """ loadings_df = pd.DataFrame( self.loadings, columns=["factor %d" % (i) for i in range(self.loadings.shape[1])], index=self.endog_names ) if style not in ['raw', 'display', 'strings']: msg = "style has to be one of 'raw', 'display', 'strings'" raise ValueError(msg) if style == 'raw': return loadings_df # add sorting and some formatting if sort_ is True: loadings_df2 = loadings_df.copy() n_f = len(loadings_df2) high = np.abs(loadings_df2.values).argmax(1) loadings_df2['high'] = high loadings_df2['largest'] = np.abs(loadings_df.values[np.arange(n_f), high]) loadings_df2.sort_values(by=['high', 'largest'], ascending=[True, False], inplace=True) loadings_df = loadings_df2.drop(['high', 'largest'], axis=1) if style == 'display': sty = None if threshold > 0: def color_white_small(val): """ Takes a scalar and returns a string with the css property `'color: white'` for small values, black otherwise. takes threshold from outer scope """ color = 'white' if np.abs(val) < threshold else 'black' return 'color: %s' % color sty = if highlight_max is True: def highlight_max(s): ''' highlight the maximum in a Series yellow. ''' s = np.abs(s) is_max = s == s.max() return ['background-color: '+ color_max if v else '' for v in is_max] if sty is None: sty = sty = sty.apply(highlight_max, axis=1) if decimals is not None: if sty is None: sty = sty.format("{:.%sf}" % decimals) if sty is None: return loadings_df else: return sty if style == 'strings': ld = loadings_df if decimals is not None: ld = ld.round(decimals) ld = ld.astype(str) if threshold > 0: ld[loadings_df.abs() < threshold] = '' return ld
[docs] def plot_scree(self, ncomp=None): """ Plot of the ordered eigenvalues and variance explained for the loadings Parameters ---------- ncomp : int, optional Number of loadings to include in the plot. If None, will included the same as the number of maximum possible loadings Returns ------- fig : figure Handle to the figure """ if missing_matplotlib: raise ImportError("Matplotlib missing") return plot_scree(self.eigenvals, self.n_comp, ncomp)
[docs] def plot_loadings(self, loading_pairs=None, plot_prerotated=False): """ Plot factor loadings in 2-d plots Parameters ---------- loading_pairs : None or a list of tuples Specify plots. Each tuple (i, j) represent one figure, i and j is the loading number for x-axis and y-axis, respectively. If `None`, all combinations of the loadings will be plotted. plot_prerotated : True or False If True, the loadings before rotation applied will be plotted. If False, rotated loadings will be plotted. Returns ------- figs : a list of figure handles """ if missing_matplotlib: raise ImportError("Matplotlib missing") if self.rotation_method is None: plot_prerotated = True loadings = self.loadings_no_rot if plot_prerotated else self.loadings if plot_prerotated: title = 'Prerotated Factor Pattern' else: title = '%s Rotated Factor Pattern' % (self.rotation_method) var_explained = self.eigenvals / self.n_comp * 100 return plot_loadings(loadings, loading_pairs=loading_pairs, title=title, row_names=self.endog_names, percent_variance=var_explained)
[docs] @cache_readonly def fitted_cov(self): """ Returns the fitted covariance matrix. """ c =, self.loadings.T) c.flat[::c.shape[0]+1] += self.uniqueness return c
[docs] @cache_readonly def uniq_stderr(self, kurt=0): """ The standard errors of the uniquenesses. Parameters ---------- kurt: float Excess kurtosis Notes ----- If excess kurtosis is known, provide as `kurt`. Standard errors are only available if the model was fit using maximum likelihood. If `endog` is not provided, `nobs` must be provided to obtain standard errors. These are asymptotic standard errors. See Bai and Li (2012) for conditions under which the standard errors are valid. The standard errors are only applicable to the original, unrotated maximum likelihood solution. """ if self.fa_method.lower() != "ml": msg = "Standard errors only available under ML estimation" raise ValueError(msg) if self.nobs is None: msg = "nobs is required to obtain standard errors." raise ValueError(msg) v = self.uniqueness**2 * (2 + kurt) return np.sqrt(v / self.nobs)
[docs] @cache_readonly def load_stderr(self): """ The standard errors of the loadings. Standard errors are only available if the model was fit using maximum likelihood. If `endog` is not provided, `nobs` must be provided to obtain standard errors. These are asymptotic standard errors. See Bai and Li (2012) for conditions under which the standard errors are valid. The standard errors are only applicable to the original, unrotated maximum likelihood solution. """ if self.fa_method.lower() != "ml": msg = "Standard errors only available under ML estimation" raise ValueError(msg) if self.nobs is None: msg = "nobs is required to obtain standard errors." raise ValueError(msg) v = np.outer(self.uniqueness, np.ones(self.loadings.shape[1])) return np.sqrt(v / self.nobs)