Default is c_## for ## in p the number of regressors
alpha : float
significance level for the confidence intervals. Default is
alpha = 0.05 which implies a confidence level of 95%.
title : string, optional
Title for the params table. If not None, then this replaces the
default title
Returns:
smry : string or Summary instance
This contains a parameter results table in the case of t or z test
in the same form as the parameter results table in the model
results summary.
For F or Wald test, the return is a string.