Standard deviation is the square root of the variance of a random variable, an estimator thereof, or a similar measure of the spread of a batch of data.

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How to calculate the weighted standard deviation [duplicate]

I have found many equations which claim to be for weighted standard deviation, yet all of these differ very slightly, and I am confused as to which is the correct one. I have some data in Excel, and ...
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2answers
143 views

The average of mean and standard deviation

I have the mean and standard deviation for body temperature ( in a group of people n=10 ), which measured using a thermometer in the left axilla, then in the right axilla ...
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9 views

Find standard deviation of all points if i have 2 samples mean and stdev [duplicate]

I'm not a statistician and I need your help... ;-) I have two samples: SAMPLE1, mean1= 12.74, stdev1= 0.106 SAMPLE2, mean2= 12.89, stdev2= 0.113 SAMPLE1 is composed by 2 values n1= 12.66 and n2= ...
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52 views

How to transform standard deviations from standard deviations

so I am doing a meta-analysis & have access to height and weight data (with SDs) and am trying to transform this into BMI. This is rather straight forward for the means, but I am not sure how to ...
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1answer
58 views

Does the IQR or standard deviation change when scaling or shifting non-normal data?

I'm aware that scaling or shifting data that is normal or almost perfectly normal will not significantly change the standard deviation. Through practice I've that this is not the case with non-normal ...
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4answers
59 views

Odds of a number appearing only one time in 500 spins on roulette

I recently observed a roulette wheel where one number appeared only once in five hundred spins. This is an American roulette wheel with 0 and 00, so the odds of any number hitting should be 1/38. I ...
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12 views

Computing SD for function of two RV's in R gives wrong results [duplicate]

I have 2 random variables, all independant, discrete and uniform I want to compute standard deviation for Z = X - Y Here is the R code: ...
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1answer
29 views

Learning Statistics [closed]

I am new to statistics and I am trying to get my head around 'why' some of these are calculated the way they are and what they mean, or were they just made a preference that stuck? - the statistics ...
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1answer
33 views

Pool data from two different points of time with different attendants

I have two samples (each nurses) one from 2008 and the other drawn 2013. Both got the same questionaire to fill out. Now I would like to pool the data but do not know if I just can do it. My idea was ...
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1answer
28 views

If two stats have same stdev but different distribution will their variance be the same?

So if two distributions are, say, normally distributed and have the same standard deviation, they should have the same variance, right? How about if they aren't both normally distributed?
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27 views

Standard deviation vs Stardard error of sample mean

I am currently attempting to analyze some data, and it has been a few years since I have taken a statistics course, so I am a bit rusty at this stuff. I have a times series of 12 different sample ...
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1answer
17 views

Standard deviation in principal component space

I am running a large number of simulations in which I have a 3D parameter space, and for each set of parameters (point in the 3D space) I run 100 simulations. I then use 14 measures to quantify the ...
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10 views

Standard deviation in PPA

In Point Pattern Analysis I created a Standard deviation with a single degree (not sure what is the unit but $1\alpha$). Is there any use for counting the points within the area created? what does it ...
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9 views

Hypothesis testing for standard deviation, confused by sample standard deviation

I have a problem that strikes me as a bit weird and is causing me some confusion. A company claims that a certain standard deviation is less than 0.10. A sample of size 20 yields a sample standard ...
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1answer
34 views

Derivative and its variance, of random/probabilistic data

I have a sensor that outputs the value and variance of data. The coordinate system is almost 2D polar, except it's not: (magnitude, angle), but it's: (distance along optical center, angle from optical ...
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0answers
12 views

k.means relation between sum squared error and variance

I work with k-means algorithm and I don't understand the relation between sum squared error and variance. Is there a relation between these values?. I work with k=1. And the values are Sum squared ...
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0answers
24 views

Probability of Non-exceedance modelled by Normal Distribution Question

The complete question is: A number of pre-cast beams are to be laid side-by-side to form a bridge deck which will later receive an in-situ topping. The beams are nominally 300mm wide, but in practice ...
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2answers
85 views

Error bars, linear regression and “standard deviation” for point

I have a set of experimental data points. I performed the measurements in triplicate, for each of the point of the data set. Therefore, I can draw each data point with the standard deviation of each ...
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0answers
25 views

Plain words (non-mathematical) explanation of the difference between Confidence Intervals, Standard Error of the Mean, and Standard Deviation? [duplicate]

As the question states, I'm interested in the difference between CIs, SEM, and SD, explained in plain words (so as to be able to communicate it to people without maths/stats background). My current ...
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19 views

How to report standard deviation while averaging a dataset multiple times?

This question appears simple but it may not be. I have a year long, 1 degree, daily, 3-d global climate data set (temperature) representing different latitude, longitude, and days. That means the data ...
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1answer
102 views

What is implied by standard deviation being much larger than the mean?

What does it imply for standard deviation being more than twice the mean? Our data is timing data from event durations and so strictly positive. (Sometimes very small negatives show up due to clock ...
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17 views

Forecasting intervals linear extrapolation with time as independent variable

I want to do a forecast with linear extrapolation, and I want to make prediction intervals with it. I see a lot of prediction interval explanations, but I don't see how to use this for my kind of ...
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29 views

Four standard deviation rules in relation to normality testing

Within our department we were given a set of guidelines for how we might decide whether to proceed with parametric or non-parametric testing (for continuous data). These were drawn up in consultation ...
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3answers
62 views

Why is standard deviation defined as sqrt(var(x)) and not as abs(X-u)? [duplicate]

Why is standard deviation usually defined as sqrt(var(x)) and not simply as abs(X-u) while the latter is simpler to understand and both give same values?
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21 views

How do I test for a difference in the standard deviations of two groups?

I have two groups and I want to know if there is a difference in standard deviation (or variance if it's easier) for each parameter. Here is a table of descriptive statistics for my data: After ...
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7 views

The estimator of variance of linear regression targets

In Section 3.2 of the book The elements of Statistical Learning (2ed), I read the text: Typically one estimates the variance $\sigma^2$ by $$ \hat{\sigma}^2 = ...
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1answer
22 views

Standard deviation for weighted sum of normal distributions

I have 2 normally distributed random variable $H_0$ and $H_1$, which are combined to give the weighted distribution $H$ as follows: $H_0 \sim N(\mu_0, \sigma_0)$ $H_1 \sim N(\mu_1, \sigma_1)$ $$f_H ...
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45 views

How to calculate accuracy in cross-validation?

I have a classification problem consisting of two classes. I have around 10000 data pionts and 20 features. I'm doing nested 10-fold cross-validation. I am unsure about calculating the accuracy. I ...
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37 views

Given only the mean and the standard deviation can I find the target score to be in the top 10%

I am working backward from a government summary of how they calculated something. They give the mean and standard deviation only but the goal is to be in the top 10% of all physician providers. The ...
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21 views

Real world example where mean is multiple orders greater than the standard deviation

This question is related to my research work. As it says in the title, I wanted to know if there exist any real world examples where the mean is multiple orders of magnitude larger than the standard ...
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12 views

Calculating Standard Deviation for a change in percentage

I imagine this is a rather basic stats question but am asking for some assistance as I don't want to calculate this wrong! I have a set of baseline data (call it x) from a study and then the same ...
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36 views

Interpreting standard deviation ratio (is std deviation ratio equal to coefficient of variation?)

I am new in this area. I apologizes if my question is silly. I need to include the homogeneity and heterogeneity of variance as one of the factor in my robustness study.Therefore, i saw this phrase. ...
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1answer
20 views

Compare standard devation between different samples?

I am calculating standard deviations $\hat\sigma_i$ from many samples from distributions with mean equal to zero but different variances $N(0, \sigma_i^2)$. Each sample has different size $N$. When ...
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1answer
23 views

Standard deviation of a Bernoulli distribution?

Example: We have a population of 100 people, where only 60 of them love pizza. So, the probability of success is 0.6 SD[x] = $\sqrt{pq} = \sqrt{0.6 \times 0.4} = 0.48 $ The definition of SD is : ...
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33 views

Why do we calculate pooled standard deviations by using variances?

Why do we calculate the pooled standard deviation by averaging the variances and taking the square root, rather than averaging the standard deviations directly? Edit: this came up in the context of ...
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6 views

What should I use to establish a threshold to detect threshold crossings?

I have data graphed in green here: I want to detect the peaks but I don't know how to define the threshold values. The blue lines are mean ± standard deviation. Using that, I would miss the three ...
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77 views

What is the expected distance from the mean of a Gaussian? [duplicate]

For $p(x) = N(x|\mu,\sigma)$, what is $E[|x-\mu|]$? Is it the standard deviation $\sigma$?
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14 views

Ordered categorical variable descriptive statistics

I'm writing a report on a (fictional) randomised controlled trial, and I'm working on my first table, baseline characteristics. It's going to look more or less like this: (The values are ...
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22 views

Guarantee Period - standard deviation and mean given

I need some assistance regarding 1.2. Please can you advise whats the best solution? I seem to have worked out 1.1. The life span of an imported brand of kettles sold by an appliance giant is ...
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12 views

Error propagation: add errors in quadrature, or use a weighted standard deviation?

I have a measurement $x$ with a known uncertainty $\sigma_m$. I have a black box that can take an error-free measurement $x$ and produce a value $y$ with a known uncertainty $\sigma_{b}$ (which is ...
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39 views

Is this sample drawn from the normal distribution ? using information from both mean and standard deviation

After correcting for a bug in my code in a previous question, I could simulate efficiently thousands of samples from the normal distribution N(0,1). I calculated the mean and standard deviation of ...
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1answer
84 views

Sampling 100000 times from normal distribution in R : strange distribution of samples' standard deviation

I generated, in R, one hundred thousand random samples of ten values from the normal distribution with mean zero and unit standard deviation, and registered each mean and standard deviation, in hope ...
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18 views

Standard Deviations or Standard Errors for Adjusted Means in ANCOVA?

I think it is standard to report standard errors (SE) for adjusted means after conducting ANCOVA. However, some people claimed it is more meaningful to provide standard deviations (SD) instead of SE. ...
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29 views

Understanding Process Behind Calculation of Loss (cat model)

I currently studying event loss table (ELT) produced by RMS (Risk Management Solution) as the output of cat model. This table can be used to generate distribution of loss. Some important points ...
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42 views

Why do we need the SD line?

Why we need the SD line(magenta) and how does it help us, besides just passing through all standard units of x and ...
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1answer
17 views

Spread on x-axis around an extremum

I am working on a graph that has Power (Watts) on the x-axis and Frequency (not Hertz here, more like the probability that we consume that much power) on the y-axis. What I would like to do with it ...
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1answer
47 views

What does subscript i mean in statistics in this context (table with values included)?

This has been driving me nuts for hours. I cannot find information anywhere on the internet on what the formulas in the upper-right two cells mean. The i subscript is throwing me off.
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9 views

Calculating st dev for each group in A/B test

I work on a marketing channel for a company, and I recently ran a test that gave following results: Baseline visits: 1823 Baseline conversions: 62 Test visits: 126 Test conversions: 12 The ...
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24 views

Inter-quartile range

If we have a non-normal distribution say (Weibull) and we used a robust estimator of standard deviation in term of inter-quartile range (IQR). Is it possible we replace IQR=3*SD?
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25 views

Taylor Series to Find Expected and Variance [duplicate]

Let g(X) be a specified function of X. The first order Taylor approximation of g(X) in a neighborhood of y is g(X) squilly = g(y) + g'(y)(X-y) The right hand side is a linear function of X. Using ...