failure rate). Note that `dens' scales the output
           to be a statistical density estimate (i.e. scaled to integrate
           to 1). 'rate' estimates the rate or intensity function (events
           per unit time, or events per unit area), which may be called
           density in some fields.
         The default family is 'qgauss' if a response (y argument) has been
         provided, and 'dens' if no response is given.
    'link' Link function for local likelihood fitting. Depending on t