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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).

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.

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Estimating time

I have some data about a number of projects that have been categorized. For each project, I have the proportion of the total project length that was spent on testing. For each category, I have to estimate how long testing would likely take for any…
user81533
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How to calculate Standard Deviation of a sample

I have 100 measurements of a device being either 0 or 1. Measurements are independent. Assuming P(0) = P(1), that is probability of getting 0 is the same as getting a 1, how would I calculate standard deviation of total number of "0" measurements…
Michael
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Merging standard deviation of two groups with duplicates

I am using Parallel Algorithm (http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Parallel_algorithm) to merge standard deviation of two groups Can we merge two groups if there are duplicate entries in them example I have two groups…
banjara
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Standard deviation of concatenation of two vectors whose std are known

Let $v_1$, $v_2$ be two vectors of lengths $m$, $n$ of real numbers. Let $\sigma_1$, $\sigma_2$ be their standard deviations, and assume they are already calculated. It is possible to assume we also know the means of the vectors. Is there a $O(1)$…
Gulzar
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Standard deviation formula

I'm having a lot of doubt on the formula of the standard deviation (in linear regression). My teacher and my syllabus say it's (for $\sigma_x$): $$ \sigma_x = \sqrt{\dfrac{\displaystyle\sum (x-\bar{x})^2}{n}}$$ But my intuition tells me it's not. It…
AreTeachersDumb
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Can't find Standard Deviation for Continuous Random Variable

Here is my homework problem. Again, sorry for the formatting: A continuous random variable $X$ has a symmetric distribution with mean $18$. A brilliant mathematician has estimated that the probability that $X$ is less than $12$ is at most $12.5 %$.…
Ocasta Eshu
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How can I convert the following standard deviation formula?

Can someone please help me to convert the following standard deviation formula into something I can actually use in excel? At the moment what I do is I have to quote every single cell in my formula and with the amount of data I have to go through…
Alien_Explorer
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Finding the standard deviation of a set of angles.

My question is given a set of angles in the form of degrees minutes and seconds once finding the mean how do you find the standard deviation. I know how to find the average or mean of a set (see below) but i'm not sure how to find the standard…
Dmitri.Mendeleev
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How can I understand my standard deviation?

I have some (2749) senor output values. They range from 0 to 1769. With google spreadsheet I put it thru some calculations to get the (mean) average and standard deviation. With this I created two colums BINS and NORMDIST to create a chart. Please…
fUrious
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Sample or Poulation standard deviation

In a mobile app that I am creating the user can tap and view content in detail by tapping on headlines. I want to keep track of how "important" the user considers the content detail to be by monitoring the time they spend on it. To that end I do…
DroidOS
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Alternative to Standard Deviation as an Average Spread

I have heard on numerous occasions that the Standard Deviation of a data set is meant to represent "the average spread of the data around the mean", and if that's the case why don't we use this formula instead which yields a much more precise…
Chris Wilson
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Percentile for a Given Z-Score

Disclaimer: Statistical math person I am not... I'm a programmer that has been tasked with finding the percentile a child will fall in depending on their weight and age according to the CDC. The CDC site with the data is:…
AGoodDisplayName
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Standard Deviation - Calculating Deviation from Random Number

If I wish to calculate the average deviation from a value in a list, can I use the standard deviation equation using the value in place of the mean? If so, why? If not, what's a good alternative?
mino
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Mean and Standard Deviation

I've been struggling to solve this problem for quite some time. The solution states that the mean = 0,4% and SD = 2,5%, but I can't understand why. "The daily return on a stock has a mean of 0,2% and a standard deviation of 1,25%. We want to find…
Alan
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Finding the sum of $\left(x-\text{mean}\right)^2$

I am stumped on a question. It gives me the mean value as 24, standard deviation is 4 and N = 10. What is the sum of (x-mean)^2 What I've tried is as follow $$ \text{Standard Deviation} = \sqrt{\dfrac{\sum (x - x')^{2}}{N}} $$ $$ 4 =…
user3276954
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