def _get_marker_style(obs_stat, p, one_sided_lower):
    """Returns matplotlib marker style as fmt string"""
    if obs_stat < p[0] or obs_stat > p[1]:
        # red circle
        fmt = 'ro'
    else:
        # green square
        fmt = 'gs'
    if one_sided_lower:
        if obs_stat < p[0]:
            fmt = 'ro'
        else:
            fmt = 'gs'
    return fmt