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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Moss scheduling Simulator and Standard Deviation in plain english?

source : http://www.ontko.com/moss/sched/user_guide.html Configuration File Options standdev n * The number of standard deviations from the average length of time a process should execute ...
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rate of convergence of mean ,variance & skewness estimators

We are asked a question which of mean,variance or skewness converges faster. At first I thought it was straight forward answer: mean->variance->skewness. But I am not sure anymore because I read ...
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Average, standard deviation and min/max values

I'm analzying a computer science paper and just found in the experimental setup the following statement: Average (standard deviation) of number of files per peer: 464 (554) Min - max number of files ...
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flares probability

There are 33 no of flares distributed in 2 hemisphere north and south. the no of flares in north hemisphere is 14 and no of flares in southern hemisphere is 19. then how to find the probability of ...
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Calculating missing data points from standard deviation and mean

I have to figure out what to missing data points are from a set of 10 scores. The mean of the 10 observed scores is 20.0 and the standard deviation is 6.0. The observed scores are listed below, with ...
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162 views

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 ...
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How to interpret standard deviation of samples with different means?

Let be two samples collections A and B. Mean of the first is 5 and the second is 15. Standard deviation of the first is 2 and the second is 5. Can we conclude something even though the two datasets ...
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Which is a better measure of uncertainty: standard deviation or resolution uncertainty?

Let's say I take a ton of measurements of the diameter of a marble with a 0.001" resolution micrometer, and I calculate the standard deviation of the sample set. Would the standard deviation be a ...
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245 views

Given a set of data (distance vs time) obtain a closer approximate for velocity

This is actually a physics experiment. I've collected a set of data Distance and time it takes for a cart to move down an incline plane. From here, I've calculated the average time (...
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1k views

Standard Deviation vs Standard Error

I am confused about the difference between standard deviation and error. When do I use which? From my lecture: Standard deviation quantifies spread of data about mean Standard error measures spread ...
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128 views

Continuously sampled event: Estimating the value of a future data point, based on past measurements and their tendency

Problem I'd appreciate some ideas on how to define a formula to estimate the value of a future data point for a continuously sampled event, based on past measurements and their tendency. At any ...
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739 views

Meaning of Empirical formula when applied to some cases

When applying the Empirical formula on a data set, for example calculating 1, 2 or 3 standard deviations below and above the mean of a data set, for some cases, this might not make sense. For example, ...
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852 views

Adjusting mean and standard deviation

There's a set of 8 bags with the following weights in grams given: 1013, 997, 1013, 1013, 1004, 985, 991, 997 The mean is 1001.625, unbiased standard deviation is 10.86. I have the following ...
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Need to calculate significance from a data set.

I have a set of data that looks like this: ...
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36 views

Extracting a function from a standard

I have a standard and I need create a function to resolve this, for example: if my $X < 21$ my $Y$ will be $24$ else if my $x < 28$ my $y$ will be $32$ ... How do I calculate a function for ...
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383 views

Aggregating standard deviation across many samples

I have data in the following form that correspond to data about sessions on a website: ID, # of actions (length), mean and standard deviation of time between actions: ...
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571 views

Statistics - Z-score confusion.

For z score, you are taking the sample value subtracting population mean and dividing it by std deviation. Is that correct so far? Now, the "sample value" is defined by an equation. In my scenario, I ...
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300 views

Variance of a max function

Say $x_1$ and $x_2$ are normal random variables with known means and standard deviations and $C$ is a constant. If $y = \max(x_1,x_2,C)$, what is $\mathrm{Var}(y)$? Well, I forgot to tell that $x_1$ ...
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Calculating the confidence interval

I've collected data such as mean $ $ and standard deviation $b$ values for several experimental studies, each of which was examined $n$ cases. I would like to report the results with the confidence ...
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normal distribution and standard deviation

1.in a normal distribution data the standard deviation is greater than the quartile deviation and the mean deviation ?? in a normal distribution 31% of the items are under 45 and 8% are over 64 find ...
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Calculate standard deviation from ratio of two variables

Ok here is my problem. For my research I am investigating if we can use twitter to create sports data. One part of the problem is for example this: We now for example that in the 6th minute of the ...
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Mean equal to standard deviation, with positive values

I read the question and the answers regarding the idea of the mean being equal to the standard deviation, in which the mean can always be adjusted to equal anything. But, if the data is restricted to ...
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When standard deviation is unknown?

I am reading a book about Statistics and I have encountered a text line: ...except in the case where standard deviation of the basic set is unknown... I am not really sure what it means, could ...
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745 views

calculate standard deviation from percentage of mean occuring.

I'm not a math person, although I find it quite interesting. I'm a programmer but I've got a math problem I'm trying to figure out. Lets assume I'm trying to create a program that will predict at ...
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190 views

Error Metric which incorporates both mean & standard deviation of data in euclidean space

For simplicities sake (the actually problem is more complex)...Let say I have a set of n 3d points, whose position move over time. For all pairs, I have calculated the mean and standard deviation of ...
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Deviation from the a level

Not really sure if it's more related to programming or maths, but.. What mathematical function can be used to determine that a deviation from a reference level has exceeded some X limit in Y time? ...
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Simple question on standard deviation and mean.

This question has kinda stumped me: For a data set, the mean is 5 and the standard deviation is 1. There are 10 values in the data set. Is the range of the data set bigger, smaller or equal to ...
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238 views

Add value to known mean and Standard deviation

I have a distribution that will continuously have numbers added to it as they are measured. I want to keep only knowledge of the mean, the standard deviation, and the number of values so far in the ...
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57 views

significance test

I've analysed newspapers by counting the language distributions of the articles. The results look like that: ...
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Remove statistical outliers

I've analysed newspapers by counting the language distributions of the articles. The results look like that: ...
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108 views

Calculating minumum representative sample

Let's say I played 500 hands in poker and earned 345 units ( dollars not, important for calculation). So on long term I'm earning 345/500 = 0.69 * 100 = 69 every 100 hand session. But 500 hands is ...
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319 views

Error propagation and averages, a practical question

Ok, I'm sure this is simple, yet I'm confused. Lets say my goal is to obtain an average concentration C=N/V so I take a number of N and V readings with errors: $N_1=50\pm2, V_1=100\pm4$ ...
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90 views

standard deviation computation

If I currently have a sum of N elements (I don't have the elements them self), their mean and the corresponding standard deviation. Later on I receive M (known) other elements. I want to update the ...
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106 views

How do i scale my errorbars when i scale my data?

I am plotting distributions of data with the standard deviation and median of my data. Now when i want to scale my median by a another variable, how do i need to modify the standart deviation?
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Normalizing a matrix using matrix operations

I need some help in normalizing my matrix. I have a 5X4 matrix A. I want to normalize each column. Following is the explanation on the operations B = Operation of matrix (A) B matrix is 5x4 matrix. ...
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Standard Deviation: Why divide by $(N-1)$ rather than $N$?

The forumlae for standard deviation seems to be the square root of the sum of the squared deviation from mean divided by $N-1$. Why isn't it simply the square root of the mean of the squared ...
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Multiplying two averages, what to do with the deviations?

If I multiply the averages of two sets of data, then what can I conclude with the deviation of that data? That is, for a given average X1 and X2, both are different sets of data but related, I ...
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Getting the correct error for a mean calculation

A constant k needs to be calculated including its gaussian error. $k = f_{(u,t)}$ $k_i$ can be calculated with the values and errors of $u_i$ and $t_i$ and their respective errors. Main issue is ...
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Prove one standard deviation lies on inflection points

Is my conjecture correct that one standard deviation lies on the inflection points of the normal distribution curve (of the probability density function)? How can it be proved using the standard ...
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Determining variance from sum of two random correlated variables

I understand that the variance of the sum of two independent normally distributed random variables is the sum of the variances, but how does this change when the two random variables are correlated? ...
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Estimate the sample deviation in one pass

We've learned this algorithm in class but I'm not sure I've fully understood the correctness of this approach. It is known as Welford's algorithm for the sum of squares, as described in: Welford, ...
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57 views

Set of numbers given, find mean and SD of the other

A set of eight numbers has mean 5 and SD 4. The number 21 and another integer n are added to the set. The standard deviation of the set is now 6. Find n and the mean of the set now.
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403 views

Normal distribution involving $\Phi(z)$ and standard deviation

The random variable X has normal distribution with mean $\mu$ and standard deviation $\sigma$. $\mathbb{P}(X>31)=0.2743$ and $\mathbb{P}(X<39)=0.9192$. Find $\mu$ and $\sigma$.
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Calculating score

I have a number of values, grouped by some category. For every category, I've calculated average and standard deviation. Now I want to calculate a score (say 1 to 1000) for every category. I don't ...
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What does it mean if the cumulative normal = 1?

What is the significance of cumulative normal = 1? I am trying to program a game, however I have inherited code from another programmer. He is using the cumulative norm. his code is outputting a ...
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incremental computation of standard deviation

How can I compute the standard deviation in an incremental way (using the new value and the last computed mean and/or std deviation) ? for the non incremental way, I just do something like: ...
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What does it mean to divide by the standard deviation?

I'm trying to variance normalise an image, in order to do so, I subtract the mean from the pixel value, to have a 0 mean, and divide by the standard deviation, to have a unit variance, right ? but ...
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How can I compare two averages of imperfect measurements, with their std. deviations?

I have a process by which I measure the times it take to do something, (run some code), and this time varies, a lot. I'm trying to optimize this code, making small changes that sometimes have small ...
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161 views

Normalising Standard Deviation as score for Burstiness calculation

I have measured the frequency of terms within the same period (say 14 days), and I wish to use Standard Deviation to calculate their burstiness (i.e. which terms are more spiky), therefore, if a term ...
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452 views

Standard Deviation algorithm for small population size?

I need to calculate the standard deviation on the entire population. The population size is 7, but for others it may be between 5-14. I see a few variance algorithms listed on Wikipedia. What stdev ...