Logarithmic Trendline - Please Help

[Chantay Thomas]

I am in the process of creating a chart and must use a
trendline that will predict future values. Currently I
have chosen to use a logarithmic trendline. Is this the
best one to use?

I am charting charting current workload by month
(example: Jan - 20; Feb - 30; - March - 23). I want to
use the trendline to predict future workload based on my
current data. Is logarithmic the best trendline to use?
Or should I use Linear?? Could someone please tell me
the different between the 2 as well
..

 

[Tushar Mehta]

The best trendline is the one that (a) correctly maps your data based on
what you know about them, and/or (b) most accurately duplicates existing
data.

So, if you believe that the predicted workload is a logarithmic function
of the indepdendent variable, you should use a log trendline. If you
believe the workload increases linearly over time (and date/time is on
the x-axis), you should use a linear trendline.

Among other things you can do is use the LINEST function (and, no, the
LINEST function is not limited to linear trendlines) since it will
provide some more statistics about the 'quality of the fit.' For more
on how to use LINEST for non-linear relations see Bernard Liengme's
http://www.stfx.ca/people/bliengme/ExcelTips/Polynomial.htm
--
Regards,

Tushar Mehta
www.tushar-mehta.com
Business solutions leveraging technology
Microsoft Most Valuable Professional (MVP) 2000-2004