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Feb 2, 2017 2:21 AM
(701 views)

Hi,

I have a question regarding the Fit Line functionality in version 13.

In version 10, I was able to make graphs with a linear regression line that extended beyond the data points (see figure). However in version 13 the linear regression line stops at the last data point. Is there a setting in version 13 to achieve the extension of the linear regression beyond the last data point?

Thanks!

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Feb 8, 2017 8:31 AM
(1258 views)

Solution

I agree with Jim's concerns about extrapolating beyond the range of data observed. However, if you wish to do this you can add in a new row to the table with a value beyond the range of data for just your X variable, and JMP will then extend the line to that point. Since there is no Y value associated with that row this will not change the regression results.

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Feb 2, 2017 3:22 AM
(678 views)

You can use either the annotation tools, or in JSL use the Add Graphics capability to add to the fit line, however, since it is a regression, which is based upon the parameters within the data, and not a forcasting tool, having the fit line project beyond the known data points would be statictically improper. So what you are seeing is a correction of an error in JMP 10.

Jim

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Feb 8, 2017 8:31 AM
(1259 views)

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Feb 9, 2017 12:57 AM
(620 views)

Highlighted
Adding a 0 on x didn't work. Had to use Annotation tools with fit where intercept is forced to zero where it is impossible to have any other intercept value other than (0,0).

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Feb 17, 2017 8:50 AM
(591 views)

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Feb 17, 2017 8:56 AM
(589 views)

There are, obviously, times where you want to force the intercept to 0, but a caution: this changes the interpretation of many of the regression statistics that you are looking at. Essentially, by forcing the intercept to be 0, you are saying that the mean is 0 (think of centered/scaled data). This can be especially problematic if you are extrapolating beyond the range of your data.

Another simple way to think of this: think of a plot of height versus weight. You can fit a line to that data. Should that line be forced to go through the (0,0) point? If you have no height, you would not have a weight so it makes sense. However, the linear relationship likely would not hold from the lowest height datapoint to 0. Forcing it to be linear across the entire range can cause problems.

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Feb 17, 2017 9:08 AM
(586 views)

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Feb 17, 2017 9:12 AM
(583 views)

You can use **Bivariate** > **Fit Special** command to select a No Intercept trend analysis.