
#1
Sep2507, 05:02 PM

HW Helper
P: 6,214

Now I know that [tex]\sigma=\sqrt{var(x)}[/tex]
which simplifies to this expression : [tex]\sigma=\sqrt{\frac{1}{N}\sum_{i=1}^{N}(x\overline{x})^2}[/tex] can someone show me how they got such an expression? and in chemistry I have to use a standard deviation calculation to get out a problem. Now normally I would use the above equation but my notes tell me to use this equation: [tex]\sigma=\sqrt{\frac{1}{N1}\sum_{i=1}^{N}(x\overline{x})^2}[/tex] Which one is correct to use? and can someone tell me if this is correct [tex]c_v =\frac{\sigma}{\overline{x}}[/tex] where [tex]c_v[/tex] is the coefficient of variation 



#2
Sep2507, 08:22 PM

Sci Advisor
P: 5,941

The definition of the st. dev. depends on whether or not the mean is the true mean or the average of the experimental data. For the true mean use 1/N, for the experimental average use 1/(N1). If you take the average of the variance with the experimental mean and compare it to the average of the variance with the true mean, you will see they are equal.




#3
Sep2507, 08:28 PM

HW Helper
P: 6,214

Oh I see now,thank you



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