'estimate model by minimizing negative loglikelihood
does this need to be overwritten ?'

def fit(self, start_params=None, maxiter=5000, method='fmin', tol=1e-08):

    if ((start_params is None) and hasattr(self, '_start_params')):
        start_params = self._start_params
    mlefit = super(TSMLEModel, self).fit(start_params=start_params, maxiter=maxiter, method=method, tol=tol)
    return mlefit
