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Is there a formula for simple linear regression

Posted on 2011-09-09
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Last Modified: 2012-05-12
I have two columns data like below
A        B
1.2     0.518
4.6     0.776
5.6     0.805

3.8       ?(should be between 0.518 and 0.776, any formula I can use?)

Now I want to calculate data B when A = 3.8 and suppose it is linear relation
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Question by:jjxia2001
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StephenJR earned 500 total points
ID: 36512900
If 3.8 is in A4 then I think this works

=B1+(A4-A1)/(A2-A1)*(B2-B1)

Btw this is interpolation, not regression.
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Author Comment

by:jjxia2001
ID: 36512943
I used the similar formula, but I want to know if there is a function built inside Excel that I can use.
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Expert Comment

by:StephenJR
ID: 36512962
Nothing built in.
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LVL 50

Expert Comment

by:barry houdini
ID: 36513134
of course that formula assumes that you already know that 3.8 falls between A1 and A2. If that you need the formula to work unaltered for other values, e.g. if A4 = 4.8 then you can use this formula

=FORECAST(A4,OFFSET(B1:B3,MATCH(A4,A1:A3)-1,0,2,1),OFFSET(A1:A3,MATCH(A4,A1:A3)-1,0,2,1))

A4 must be >=A1 and < A3

regards, barry
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Expert Comment

by:byundt
ID: 36513139
Is there a function built into Excel? Of course there is--the TREND function. You use like this:
=TREND(B2:B4,A2:A4,D2)
=TREND(KnownX, KnownY, NewX)         returns Predicted Y

TREND does a linear regression to make its prediction, and can handle more than one X variable if necessary.
TrendFunctionQ27300562.xlsx
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Author Comment

by:jjxia2001
ID: 36513178
This is great! This is what I'm looking for!  
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Expert Comment

by:byundt
ID: 36513204
I misspoke. The format for TREND is:
=TREND(KnownY, KnownX, NewX)         returns Predicted Y

The sample workbook and suggested formula with addresses were both correct, however.
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Expert Comment

by:barry houdini
ID: 36513222
Hi Brad,

Surely TREND doesn't give your linear interpolation (unless the known Xs and known Ys are only 2 value ranges)? If you use 4.6 in D2, i.e. one of the A2:A4 values then wouldn't you expect the result to be the corresponding B2:B4 value, i.e. 0.776 - with TREND you get 0.754

For the original sample you can also use LOOKUP for linear interpolation, i.e. this will do the same as the FORECAST function I posted

=LOOKUP(A4,A1:A2,B1:B2+(B2:B3-B1:B2)*(A4-A1:A2)/(A2:A3-A1:A2))

regards, barry
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Expert Comment

by:barry houdini
ID: 36513410
See attached file which demonstrates the different results obtained. There are random X and Y values in A2:B9 and (mostly) random "lookup values" in D2:D6. Press F9 key to re-generate random numbers

regards, barry
interpolation.xlsx
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