• We’re currently investigating an issue related to the forum theme and styling that is impacting page layout and visual formatting. The problem has been identified, and we are actively working on a resolution. There is no impact to user data or functionality, this is strictly a front-end display issue. We’ll post an update once the fix has been deployed. Thanks for your patience while we get this sorted.

Standard deviation question ...

Page 2 - Seeking answers? Join the AnandTech community: where nearly half-a-million members share solutions and discuss the latest tech.
?

Edit: That was a square in both CharMap.exe and in the post preview. 🙁

How's this?
_
| |
¯

Edit 2: That sucks. 🙁
 
Actually. I made a mistake. That should be
VAR(3 weeks sales)=VAR(wk 1+wk 2+wk 3)=VAR(wk 1)+VAR(wk 2)+VAR(wk 3)+2*COVARIANCE(wk1, wk2)+2*COVARIANCE(wk1, wk3)+ 2*COVARIANCE(wk2, wk3)


Assuming sales of week 1, 2 and 3 are independent, then it = VAR(wk1)+VAR(wk1)+VAR(wk1)=12 since COVARIANCE of any 2 independent variables=0. (TuxDave is correct under independence assumption)

In reality, the sales in three consecutive weeks are usually not independent. Factors like promotions, time of year, will make the 3 consecutive weeks behave similar in sales. If dependence is assumed, then the VAR can be as large as 36.

To sum up, the variance of the sales of a 3 week period = from 12 (if independence from week to week) to 36 (if total dependence among the 3 weeks).
 
You must log in or register to reply here.

TRENDING THREADS

Back
Top