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Calculating standard deviation of histogram

How should I calculate the standard deviation of a histogram;

Am i ok to use the midpoint of the class width and calculate the frequency of each bar and presume every value of that bar is the midpoint to find out the sum of x and the sum of x^2 and subsequently use

σ=Σx2n−(Σx)2n \sigma=\sqrt{\frac{\Sigma x^2}{n}-\frac{(\Sigma x)^2}{n}}
(edited 8 years ago)
Reply 1
Original post by Astrtricks
How should I calculate the standard deviation of a histogram;

Am i ok to use the midpoint of the class width and calculate the frequency of each bar and presume every value of that bar is the midpoint to find out the sum of x and the sum of x^2 and subsequently use

σ=Σx2n−(Σx)2n \sigma=\frac{\Sigma x^2}{n}-\frac{(\Sigma x)^2}{n}


Yep, precisely that.
Reply 2
Original post by Astrtricks
How should I calculate the standard deviation of a histogram;

Am i ok to use the midpoint of the class width and calculate the frequency of each bar and presume every value of that bar is the midpoint to find out the sum of x and the sum of x^2 and subsequently use

σ=Σx2n−(Σx)2n \sigma=\frac{\Sigma x^2}{n}-\frac{(\Sigma x)^2}{n}


You forgot the square root!!!!!

Spoiler

Reply 3
Original post by aymanzayedmannan
You forgot the square root!!!!!

Spoiler



I did think this when I was doing it because, I checked it with the answer that I got by using the table in my calculator was the square root of my answer, I'll change it.
Thanks

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