Non-linear Trendlines

[corus]

In excel why is it that certain trendline options in Excel, such as logarithmic or exponential, don't appear when you have sufficient data to perform such an analysis?

corus

 

[pmover]

i do not quite understand your question, but there are exponential and logarithmic (among others) trendline features incorporated into excel.

simply select the series and right-click mouse. choose add trendline and note the two tabs.

good luck!
-pmover

 

[corus]

thanks pmover but when you select the trendline only a certain number of the available options become available. A linear trendline always appears, as does a polynomial but the exponential, logarithmic, and power options are often greyed out and cannot be selected even though there are more than enough data points for a regression analysis to be performed. Why is that?

corus

 

[IRstuff]

There is something wrong in your installation, perhaps..

On mine, the only thing that grays out is moving average, and that's only if there are only two datapoints.

TTFN

 

[GregLocock]

negative values may kill logarthmics and so on. Given the rumoured flakiness of these trendlines I'd be inclined to roll my own anyway.

Cheers

Greg Locock

 

[jhardy1]

As GregLocock says, Excel can only calculate Trendlines when the range of x and y data is within allowable limits. Zero and negative values will make some options unavailable, but linear and polynomial fits should always be available.

 

[Latexman]

I've noticed that the trendline in my Excel 2003 is smarter than the previous version I had. It seems to make active only those trendlines that fit the data reasonable well. For example, I generated y = log (x) data and put that onto a graph and the log trendline became active. Some others were active too, but the log was not active on a previous data set I had.

Good luck,
Latexman

 

[corus]

Thanks, you're right, a negative number had slipped in unobtrusively.

corus