b is SLOPE(y,x)
a is INTERCEPT(y,x)
which are available as separate functions in Excel. Start with them and
build your way up.

In Excel 2003 the calculation formula was rearranged and a misprint was
introduced into Help for FORECAST (also in Help for SLOPE and INTERCEPT),
x(bar) and y(bar) are the sample means, x and y are the individual
observations.

You might also get some useful information from
http://groups.google.com/group/micro...a03470e7a1c650

Jerry

"Sumit Kumar" wrote:

Hello David,

Please see the below formula which i took from excel help: -

The equation for FORECAST is a+bx, whe
a=y(bar) - bx(bar)
and:
b=Summation of{(x-x(bar)) (y-y(bar))} / Summation of (x-x(bar)) power2

and where x and y are the sample means AVERAGE(known_x's) and AVERAGE(known
y's).

So if X & Y are the average values then i want to know what x(bar)
& Y (bar) stand for ?

Please see the excel formula for FORECAST method incase the above formula is
not clearly stated.

"David Biddulph" wrote:

X bar is the average X value, and Y bar is the average Y value.
--
David Biddulph

"Sumit Kumar" wrote in message
...
Hello ,
I need to use forecast formula outside excel.
I explored the forecast method in excel and could not figure out the
formula. X(Bar) & Y(Bar) signify what ?

Thanks in advance

"Rodney M" wrote:

No,...Excel gives me the formual, but I don't really know how to decode
that
algebraic formula enough to come up with a forcasted number. I may have
phased my question incorrectly though.
I think that we figured out the answer though:
Jan(1) - 3; Feb(2) - 6; March(3) - 9...
Plugging the number into this equation will give you the next forcasted
number (given any two months): y3 = (((y2-y1)/(x2-x1))*(x3-x1))+y1

Example: Third month sales (y3) equals (2nd month sales (y2) minus 1st
month
sales (y1) divided by 2nd month (x2) minus 1st month (x1)) times (3rd
month
(x3) minus 1st month (x1)) plus 1st month sales (y1)

Thanks

"Dave F" wrote:

Haven't you answered your own question here?

Dave
--
A hint to posters: Specific, detailed questions are more likely to be
answered than questions that provide no detail about your problem.


"Rodney M" wrote:

Hello All,
Background: I am trying to figure out how to project my sales numbers
for
the year, given a few monthly entries. In Excel I can use the Forcast
function, but I am working in MS Access.

Question: Does anyone know how to break down the way that the Excel
Forcast
function predicts it's next value given previous values?

Example: Jan - 2; Feb - 4; March - 6. The rest of the year's numbers
should
project to....Apr - 8; May - 10; June - 12; July - 14 ...etc.

The equation for FORECAST is a+bx, whe
a = y - bx
AND
b = (sum(x-x)(y-y)/sum(x-x)^2)
AND
where x and y are the sameple means AVERAGE(known_x's) and
AVERAGE(known_y's)

Thanks for any assistance

Rodney