<p>I was able to reproduce the problem with a line or column chart, but not a scatter chart. With the line or column chart, whenever I change the backward forecast number, Excel sets it back to zero. With a scatter chart, I can do as I like.</p>
<p>Consider a very ugly workaround. Temporarily change your chart to a scatter chart, enter the desired backward forecast, and then change back to your original chart type. Excel will remember this backward forecast entry, but won't let you change it, except to zero (unless you do the scatter chart trick again).</p>

CC BY-SA 4.0
2024-02-15T00:49:40.870Z
2024-02-15T00:49:40.870Z
Richard
<p>I have a problem. I have a couple of time series for which data starts from 1995.  I need 15 more years backward (i.e.: I need data from 1980) but I cannot find them, so I decided to run an estimate based on the trendline of the data that I have. The problem is that I cannot set a backward trendline using Excel 2010, since when I try to do so the software does not let me to set the period I wanted to &quot;forecast&quot; back. So, what I have to do in order to resolve this problem?</p>
<p>P.S.: linear forecasting does not work here, because my data follow a polynomial trend of sixth grade.</p>
<p>Thanks in advance!</p>

CC BY-SA 4.0
2021-09-18T14:10:02.920Z
1. Have you considered using another program? If you insist on Excel, how about relabeling the years in a backwards order to fool Excel?
Giskard
CC BY-SA 4.0
2021-09-18T14:11:02.003Z
2. 6 variables on 25 data points sounds like overfitting.
Giskard
CC BY-SA 4.0
2021-09-18T16:18:37.103Z
Forecasting 15 years backward from 25 years, with data on yearly frequency, is pointless unless you are doing it just for fun, nobody would take that sort extrapolation seriously
1muflon1
<forecasting>
Backward trendline in Excel 2010
Giord
# Backward trendline in Excel 2010

(Asked by: username_0 on 2021-09-18)

I have a problem. I have a couple of time series for which data starts from 1995. I need 15 more years backward (i.e.: I need data from 1980) but I cannot find them, so I decided to run an estimate based on the trendline of the data that I have. The problem is that I cannot set a backward trendline using Excel 2010, since when I try to do so the software does not let me to set the period I wanted to "forecast" back. So, what I have to do in order to resolve this problem?

P.S.: linear forecasting does not work here, because my data follow a polynomial trend of sixth grade.

Thanks in advance!

**Tags:** forecasting
> **Comments:**
> **username_1**: 1. Have you considered using another program? If you insist on Excel, how about relabeling the years in a backwards order to fool Excel?  
> **username_1**: 2. 6 variables on 25 data points sounds like overfitting.  
> **username_2**: Forecasting 15 years backward from 25 years, with data on yearly frequency, is pointless unless you are doing it just for fun, nobody would take that sort extrapolation seriously  

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## 1 answers

### Answer by username_3 on 2024-02-15. Score: 0

I was able to reproduce the problem with a line or column chart, but not a scatter chart. With the line or column chart, whenever I change the backward forecast number, Excel sets it back to zero. With a scatter chart, I can do as I like.

Consider a very ugly workaround. Temporarily change your chart to a scatter chart, enter the desired backward forecast, and then change back to your original chart type. Excel will remember this backward forecast entry, but won't let you change it, except to zero (unless you do the scatter chart trick again).


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