Any one of a number of functional forms (such as the <a href="search.pl?p=logistic">logistic</a> curve) that starts out slowly but at an increasing rate, but then the rate slows as it approaches an asymptote (see <a href="search.pl?p=saturation level">saturation level</a>).&nbsp; Such curves can be used to capture a <a href="search.pl?p=diffusion">diffusion</a> process, as described in Meade and Islam (2001).<o:p></o:p></P>
<ul>
  <li>Meade, N. &amp; T. Islam (2001), “Forecasting the 
diffusion of innovations: Implications for time-series extrapolation,” in J. S. 
Armstrong (ed.), <I>Principles of Forecasting</I>. Norwell, MA: Kluwer Academic 
Press.</li>
</ul>