# Questions tagged [standard-deviation]

In Probability and Statistics, the standard deviation of a statistical population or data set is a measure of how much variation or dispersion exists from its average value. It is defined as the square root of the variance. Use this tag alongside (statistics).

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### Variability calculation based on standard deviation

I need assistance with calculating the standard deviation for a list of items, where the monthly consumption needs over the past 12 months are detailed for each item. My objective is to classify these ...
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### Calculate standard deviation for difference of two populations

I have two populations, let's say $P_1$ and $P_2$, and they have their own standard deviations, like $STD_1$ and $STD_2$. From this populations I need to calculate which one is better. I do that by ...
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### Computing error bars for the geometric mean across multiple datasets

I apologize because my understanding of statistics is somewhat basic. I will try to describe the problem as well as I can. My colleagues and I have a graph where we measure the relative performance of ...
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### Calculate the uncertainty from the geometric mean and geometric standard deviation

I'm working on a database that provide for each entry a geometric mean value as well as a geometric standard deviation. I would like to transform this value into an approximate relative uncertainty. ...
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### Is the average distance from the average statistically meaningful?

Where this value is defined as $$\frac{1}{n} \cdot \sum_{i=1}^{n} |\overline{x} - x_i|$$ does it have any significance or use in statistics?
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### Percentage of values between 3 standard deviations and 4 standard deviations.

After learning about the empirical rule / 68-95-99.7 rule, I am just wondering about the percentage of values 4 standard deviations from the mean. This question is pretty much the same as the ...
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### Standard deviation in 3d space

Is there anything analogous to the standard deviation, but in three-dimensional space? I have two set of data SET A 3D coordinates point X Y Z a1 2.09 -1.2 4.03 b1 7.31 8.5 -2.8 c1 -3.45 1.12 9....
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I am a teacher and we now had our end-of-semester exam in which $N$ students participated. I have $k$ graders each graded a certain amount of exams $N_i$, so $\sum_{i=1}^kN_i=N$. When I check the ...
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### How to prove the inequality for the standard deviation of a linear combination of two random variables

The question comes from ‘Mathematics for Finance: An Introduction to Financial Engineering’ by Marek Capiński (Author), Tomasz Zastawniak. The book provides a conclusion about the risk and return of ...
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### What is the intuitive difference between covariance and the product of the standard deviations of bivariate data?

Can someone help me understand what the difference is—intuitively—between these concepts? Here's how I currently think of these things. The covariance, represented by: ... is essentially a mean area, ...
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### Problem with deriving a standard deviation function

I have a function which depicts errors for a specific parameter. The function for the standard deviation of this parameter is also given, but I am having problems deriving it from the error function. ...
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