Standard Deviation in Excel

[ChipsAhoya]

I know what STD is an all, but I'm not the best with Excel, and I was just wondering if anyone know how to input a standard deviation formula that would be weighted. In my sheet, I have one column with the win/loss for the session, and one column for the # of hours in the session.

I know I need to have it like (1/N)Exi form, but I have no idea how to program that... Do I need to have a separate column for (session i's hours) / (total hours)?

Thanks for any help...

have a nice day,
ChipsAhoya

[BruceZ]

[ QUOTE ]
I know what STD is an all, but I'm not the best with Excel, and I was just wondering if anyone know how to input a standard deviation formula that would be weighted. In my sheet, I have one column with the win/loss for the session, and one column for the # of hours in the session.

I know I need to have it like (1/N)Exi form, but I have no idea how to program that... Do I need to have a separate column for (session i's hours) / (total hours)?

Thanks for any help...

have a nice day,
ChipsAhoya

[/ QUOTE ]

If you PM me with an email address, I can send you an Excel spreadsheet that does this, along with an essay by Mason that explains the formula, and my own derivation.

The short answer is that (in your notation):

sigma^2 = (1/N)E(Xi - uTi)^2/Ti

where E means summation over N sessions, Xi is the result of the ith session, u is the average hourly rate, and Ti is the length of the ith session.