An extension of single <a href="search.pl?p=exponential smoothing">exponential smoothing</a> that allows for trends in the data. It uses two smoothing parameters, one for the level and one for the trend. (See discussion in Armstrong 2001c.)<o:p></o:p></P>
 <ul>
   <li>Armstrong, J. S. (2001c), “Extrapolation for time-series 
and cross-sectional data,” in J. S. Armstrong (ed.), <I>Principles of 
Forecasting</I>. Norwell, MA: Kluwer Academic Press.</li>
 </ul>