Calculating Exponential Function slope, using only partial data
Calculating Exponential Function slope, using only partial data
(OP)
Here's the situation: We're trying to project growth over a few years using our past data for reference. Simple exponential trendline, right? The problem is that in the last two weeks, we saw a massive jump which was out of average and will likely not happen again.
If I was using a linear trendline, it would be easy. I just calculate the slope using past data and apply it to the function. Is there a similar way to figure this out with an exponential tredline?
If I was using a linear trendline, it would be easy. I just calculate the slope using past data and apply it to the function. Is there a similar way to figure this out with an exponential tredline?





RE: Calculating Exponential Function slope, using only partial data
Good luck,
Latexman
RE: Calculating Exponential Function slope, using only partial data
Here's an example:
Let's say every week, I'm increasing exponentially by 1. So it goes as such:
1,2,4,8,16,32,etc...
But two weeks, it's off by a lot:
1,2,4,8,16,58,65, etc...
How can I figure out the growth slope, without considering the extraordinary data entries?
RE: Calculating Exponential Function slope, using only partial data
I put a zero in for the "suspect" data point. Whether it is really bad data or bad model is up to you to decide.
This type approach is also sensitive to the initial value guesses that you put into alpha and beta (like most solver problems).
=====================================
(2B)+(2B)' ?
RE: Calculating Exponential Function slope, using only partial data
"I put a zero in for the suspect data point"
should've been:
"I put a zero [b[weighting factor [/b]in for the suspect data point"
=====================================
(2B)+(2B)' ?
RE: Calculating Exponential Function slope, using only partial data
RE: Calculating Exponential Function slope, using only partial data
RE: Calculating Exponential Function slope, using only partial data
Good luck,
Latexman
RE: Calculating Exponential Function slope, using only partial data
I constructed the "slope" based on prior data. Then, I added the difference between the last data point in the list and the data point not in the list. Therefore, it'll include the increase in data, without affecting the slope.
RE: Calculating Exponential Function slope, using only partial data
Best regards
Morten
RE: Calculating Exponential Function slope, using only partial data
(He who Grubbs around among the outliers often bites off more than he can chew.)
RE: Calculating Exponential Function slope, using only partial data
RE: Calculating Exponential Function slope, using only partial data
Good luck,
Latexman
RE: Calculating Exponential Function slope, using only partial data
Plot the true data as a curve using markers only, and the edited column the same. Add a trend line to the second. That way you'll have your neat little trend line without the outliers, but they are still visible on the graph.
Cheers
Greg Locock
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