Trend: Logarithmic and Polynomial

**nsd3** · 08-28-2009, 03:58 PM

Hi,

I've tried the Trend Function on Cell H3 of the attached file but it was giving me "#Value!" as a result! Also tried putting it as array but to no avail.

Is there any formula that can derive the logarithmic and polynomial Forecast for the coming year in Excel? I can add the trendline on the chart but the line doesn't give me the values on the chart. Anyway, can anyone help to have the 2 Trend numbers on Cell H3 and I3?

Thanks in advance for your cooperation. Cheers!

**shg** · 08-28-2009, 07:55 PM

I don't think a logarithmic foecast makes much sense. Things that have a constant percentage Y/Y growth or decline follow an exponential curve. To get a prediction for 2010 that way, use =GROWTH(B3:G3, , 7), where 7 is the next number in the categorical series (2004=1, 2005=2, ...).

The 2009 YTD number has to be corrected (via extrapolation) to a 2009 total in order to be meaningfully used.

**nsd3** · 08-29-2009, 10:32 AM

Thanks for the formula to estimate the forecast on exponential curve. However, I still need Logarithmic one as other brands (not mentioned in the table) have both highs and lows during the last 6 years. The Trend Formula is not working on the Sheet as mentioned earlier. But the Logarithmic one would be really useful.

Thanks a lot.

**shg** · 08-29-2009, 01:00 PM

=trend(b3:g3, ln({1,2,3,4,5,6}), ln(7))

**nsd3** · 08-29-2009, 10:02 PM

shg, Thanks for the formula for the logarithmic trend

For cell I3, could you please give me the formula for the Polynomial Trend as some brands have seasonal impact in the year.

Thanks heaps. I really appreciate your help.