'Try to construct a basic summary instance.
Parameters
results : Model results instance
alpha : float
significance level for the confidence intervals (optional)
float_formatting: string
Float formatting for summary of parameters (optional)
title : string
Title of the summary table (optional)
xname : List of strings of length equal to the number of parameters
Names of the independent variables (optional)
yname : string
Name of the dependent variable (optional)'

def add_base(self, results, alpha=0.05, float_format='%.4f', title=None, xname=None, yname=None):

    param = summary_params(results, alpha=alpha, use_t=results.use_t)
    info = summary_model(results)
    if (xname is not None):
        param.index = xname
    if (yname is not None):
        info['Dependent    Variable:'] = yname
    self.add_dict(info, align='l')
    self.add_df(param, float_format=float_format)
    self.add_title(title=title, results=results)
