from typing import List


def get_lower_upper_percentiles(alpha: float) -> List[float]:
    """
    Returns the lower and upper quantile values for the chosen `alpha` value.

    Args
    ----
      alpha: float
         Sets the size of the credible interval. If `alpha=0.05` then extracts the
         95% credible interval for forecasts.

    Returns
    -------
      List[float]
          First value is the lower quantile and second value is upper.
    """
    return [alpha * 100. / 2., 100 - alpha * 100. / 2.]