@staticmethod
def too_small(x, tol=0.2):
    """
        Checks whether a pd.Series has any 0s or "too many" ones
        Inputs:
            x is pd.Series
            tol is the percentage of ones allowable (default=20%)
        Returns:
            True/False
        """
    num_0 = x.eq(0).sum()
    num_1 = x.eq(1).sum() / x.count()
    if num_0 > 0 or num_1 > tol:
        return True
    else:
        return False
