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Non-linear Trendlines

Non-linear Trendlines

(OP)
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

RE: Non-linear Trendlines

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

RE: Non-linear Trendlines

(OP)
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

RE: Non-linear Trendlines

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

RE: Non-linear Trendlines

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

RE: Non-linear Trendlines

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.

RE: Non-linear Trendlines

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

RE: Non-linear Trendlines

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

corus

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