def find_outlier(series, k=1.5):
    """Find outlier using first and third quartiles and interquartile range.
    Parameters
    ----------
    series: A pandas Series to find outlier in
    k: (optional) An integer indicating threshold of outlier in IQR from Q1/Q3
    Returns
    -------
    A pandas Series containing boolean values where True indicates an outlier.
    """
    q1 = series.quantile(.25)
    q3 = series.quantile(.75)
    iqr = q3-q1
    lower_bound = q1 - k*iqr
    upper_bound = q3 + k*iqr
    is_outlier = (series<lower_bound) | (series>upper_bound)
    return is_outlier