Can someone explain the STANDARD DEVIATION OF THE DIFFERENCES formula to me?

- anonymous

Can someone explain the STANDARD DEVIATION OF THE DIFFERENCES formula to me?

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- anonymous

@jagatuba @Jemurray3 @jhonyy9 @karatechopper @phi @robtobey @satellite73

- anonymous

http://www.google.com/imgres?um=1&hl=en&sa=N&biw=1440&bih=809&tbm=isch&tbnid=EWj_RcUArXWHWM:&imgrefurl=http://www.socialresearchmethods.net/kb/statdesc.php&docid=jsqc7fluc6WZ7M&imgurl=http://www.socialresearchmethods.net/kb/Assets/images/statdes3.gif&w=474&h=300&ei=q6aNUJK4C5S08ATpvoGACg&zoom=1&iact=rc&dur=392&sig=112477054274050808931&page=1&tbnh=124&tbnw=198&start=0&ndsp=21&ved=1t:429,r:0,s:0,i:71&tx=156&ty=39

- anonymous

I am given 2 sets of 10 numbers. How do I plug them into this formula to get the correct answer?

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- jhonyy9

so what numbers you have got for ????

- anonymous

##### 1 Attachment

- jhonyy9

the sum across the values how you can get it ?

- anonymous

im confused about the top part of the formula. ive been getting the wrong answers so i must be doing something wrong.

- jhonyy9

sorry but this attachement i not can opening ,not id compatibly with my excell programm

- anonymous

##### 1 Attachment

- anonymous

what about now?

- jhonyy9

can you rewrite me here the values for x and X the mean or average and the value for n ?

- jhonyy9

@robtobey can you opening this attachement please ?

- anonymous

(column 1) x = 129, 237, 110, 32, 322, 134, 119, 32, 172, 149
total sum for x = 1436
mean for x = 143.6
(column 2) y = 130, 224, 113, 38, 320, 124, 122, 33, 169, 148
total sum for y = 1421
mean for y = 142.1
value for n = 10
df = n-1 (so 9)

- jhonyy9

have you any idea for this ?

- anonymous

yes but ive been getting the wrong answers.
d bar = 1.5
so ive been doing ((129-1.5)^2+(237-1.5)^2+(110-1.5)^2+.......))

- jhonyy9

so how i see it there will be in numerator sqrt(sum(x-X)^2)
divide by sqrt9 so divide by 3
ok ?

- jhonyy9

can you calcule first this sum ?

- jhonyy9

how many will be this sum ?

- anonymous

i got 270258.5 for x
and 261262.5 for y
then i subtracted the 2 to get 8996

- anonymous

then divide by 9 and square root it to get 31.616

- anonymous

but thats wrong

- jhonyy9

why divide by 9 and not by 3 ?

- anonymous

arent u supposed to do whats in the radical first and then square root it?

- jhonyy9

why you can separte it sqrt of numerator and sqrt of denominator and vide it after

- jhonyy9

and divide it after

- anonymous

i get the same answer either way

- anonymous

31.616

- anonymous

the right answer is 5.93

- anonymous

@jhonyy9
It may to late for solving this problem. Attached is a screen capture of part of the xls file.
I am running on a mid 2010 IMac with 8Gb of ram to support virtual versions of Windows XP pro, Windows 98SE and in the past Ubuntu Linux.
The xls file is not a normal spread sheet data file. All I can provide is a screen capture of what I see.

##### 1 Attachment

- jhonyy9

how can i opening it what program i need using for ?

- anonymous

i provided all the necessary info above ^^^^^

- jhonyy9

so than you need calcule right this sum and after make the squareroot of them ,yes ?

- jhonyy9

so and after just divide it by 3

- anonymous

Ask @mariomintchev what version of Excel did she/he use to generate the spread sheet.

- anonymous

Excel 2010

- anonymous

SCREENSHOT

- phi

They want the standard deviation of the differences.
Your formula tells you how to find the standard deviation of a list of numbers.
The first step is find the list of numbers: the list of differences
so find x-y
where
x= 129, 237, 110, 32, 322, 134, 119, 32, 172, 149
y = 130, 224, 113, 38, 320, 124, 122, 33, 169, 148
the differences (call it z) are
z= -1 13 -3 -6 2 10 -3 -1 3 1
now use your formula to find the standard deviation

- anonymous

so
((-1-1.5)^2+(13-1.5)^2+(-3-1.5)^2+....)) ???

- phi

yes, then divide by 9
then take the square root.

- anonymous

ok, i got 5.95 so its close enough. thanks phi, i can always rely on you!

- phi

I got 5.930
(dd-1.5).^2
6.2500 132.2500 20.2500 56.2500 0.2500 72.2500 20.2500 6.2500 2.2500 0.2500
sum(ans)/9 = 35.1667
sqrt(35.1667)= 5.9302

- anonymous

i must have made a little mistake somewhere when punching in all of those numbers and parenthesis. i understand what i need to do now though. thanks! =o)

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