Statistics Question

[Badger]

I have a system that generates a linear trend value based on a single array of inputs.

Inputs
10
5
15
20

The outputs it gives me are:
6.5
10.5
14.5
18.5

I've no way of getting to see the actual calculation the system uses for this, so, that's my question - how do I manually calculate the output figures?

Should this be posted in Technical?

Cheers

[xoggoth]

Probably but I never bother.

I could have answered this easily once but forgotten. It appears to be a linear curve fit assuming equi spaced intervals. Look up "Least Squares" method and use it to fit straight line, y=your inputs, x=1,2,3,4.

PS With so few points hard to be sure exactly what equation used. Could try all sorts pof eqauion with least squares curve fitting orders if that don't work exactly.

[Menelaus]

Sounds like a curve fitted to OLS.

[DS23]

you want to replace the system by building your own? excel has some simple versions you can use as a starting point.

[xoggoth]

Good point. Think there is an Excel add in you need to instal for curvefits.

[Badger]

Thanks, the OLS seems plausible (if wikipedia is to be believed)

I need to manually create this in Excel, using Excel's built in functions isn't going to work, nor are any add-ins.

So I'm assuming:

Y X
1 10
2 5
3 15
4 20

I can kind of fudge the first value of 6.5 as (1+10)/2 + 1, but that's where I get stuck!

Cheers

[RichardCranium]

Input = x
Output = y

y = -0.0213x^3 + 0.88x^2 - 10.267x + 42.5

HTH

[RichardCranium]

I have a system that generates a linear trend value based on a single array of inputs.

Inputs
10
5
15
20

The outputs it gives me are:
6.5
10.5
14.5
18.5

Hang on. Shouldn't this be:
Inputs
5
10
15
20

y = 0.8x + 2.5

[RichardCranium]

You could have solved that in under two minutes by plotting it by hand on a piece of paper.

[Badger]

maybe but it's not right, starting point is 10, then 5 etc.