def logistic(x, params):
    """Evaluate logistic curve equation using log-transformed x_0.

    Parameters
    ----------
    x
        X-value at which to evaluate the logistic function.
    params : list
        * einf: maximum Y-value (effect)
        * log10_mid: log10-transformed X-value of midpoint
        * slope: Steepness of curve

    Returns
    -------
    float
        Y-value of logistic function.
    """
    einf, log10_mid, slope = params
    emin = 1.0
    mid = 10 ** log10_mid
    return ( (emin-einf) / (1 + ((x/mid)**slope) ) ) + einf