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Algorithms :: General :: linear extrapolation/Excel
By: swmrgrl86 U.S.A.  Date: 26/11/2005 21:05:49  English  Points: 20 Status: Answered
Quality : Excellent
What exactly is a linear extrapolation and how do I put it to use in Excel?
By: VGR Date: 26/11/2005 21:38:43 English  Type : Answer
it's very simple. It's a "straight line" extrapolation.
It supposes that the measure points are connected by straight lines (interpolation) and that "before" the first measure point and "after" the last point, the trend is the same as the one "in" the points group.

It's quite simple in fact. More complex models include minimizing the sum of squared error, etc

Let's take an example :
Suppose you have a table listing the population of some country in 1970, 1980, 1990 and 2000, and that you want to estimate the population in 1994. Linear interpolation tells you that the 1994 value is 4/10 (four tenth) of the difference of measure between years 2000 and 1990, plus the value of 1990 of course. So you see the point is that a straight line (proportionality rule, if you prefer) links two consequent measure points.


I think it is explained in here

As for "how to put it in eXcel", well for interpolation I think you've got the idea. For extrapolation it's not that useful. A better way to extrapolate is to use a (higher degree) polynomial interpolation.

Regards
By: VGR Date: 11/12/2005 09:33:58 English  Type : Comment
ok ? if not, then ask additional questions, if yes then accept an answer ;-)
By: OpConsole Date: 08/04/2006 09:22:08 English  Type : Comment
Hello. This is the last reminder before forced closure of the Question. Suggested choice : Accept last VGR answer.

You may Accept or Split the answer by clicking on the relevant button of the relevant comment ;-)

Regards

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