Tricky problem about std deviation calculation

[#1]

Hi all,

Suppose I have one file with

City

Region

A  (my first indicator)

B  (my second indicator)

A city belongs in only one Region. So a Region is a set of cities.

We have build an application where an user select  a city (just one), then we want to display :

(1)   the value  of  A/B   for the selected city

(2)   the value  of A/B    for  the region where the city belongs

(3)    the value of the standard deviation (stdev)   of A/B    for  the region where the city belongs

       This calculation of standard deviation is needed to get a color coding of the 1)

           if  (1)   <   (2)    - (3)   =>  color in RED

           if    (2) - (3)  <  (1) <   (2) + (3)   => color  in YELLOW

           if  (2)  +  (3)   <  (1)   =>  color in  GREEN

For (1)   no problem

For (2)   no problem   using  the P() function      Sum(  {< Region=P(Region)  >}   A ) /   Sum(  {< Region=P(Region)  >}   B )

For (3)  I can't use   of course     Stdev &  sum together,

            Indeed   we try with AGGR, but it seems AGGR  doen't works with P()

Sorry to be long, maybe someone has the solution

Regards

JJ

[CELAMBARASAN]

May be you can use this concept

SD = Squareroot(Avg)

Can you tell me standard deviation should be computed on what basis?

Can you attach a sample.

[#3]

Hi

standard deviation should be calculated like this

=  sqr(  [  (sum(  a^2/b^2)     -   (sum(a)/sum(b))^2 ) ] /  N  )    huygens formula

where N is my number of cities in the region   and  ^2  is the power 2

Of course I prefer to use  STDEV function instead  of the previous formula.

JJ

[#4]

This a sample

It seems to work with huyghens formula