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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Averaging standard deviations of unequal weight?

I'm sorry if the title is unclear, but I'm not sure of the appropriate way to phrase this question. I'm in med school (and sadly not as versed in statistics as I ought to be), and I am trying to use ...
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14 views

how to estimate scale variance only using item sd's and scale reliability

The problem I encounter is that I need to estimate the scale variance of a psychometric scale without having the original data. The only information I have is the means of the (binary) items, their ...
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2answers
38 views

Comparing two populations [Beginner]

I have sampled from two separate populations, and I want to figure out which population is better. Population 1 has an average score of 84.1 and a standard deviation of 11.8. Population 2 has an ...
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1answer
76 views

how to calculate expected sample scale mean and sd based on the means and sd's of its dichotomous items?

I am developing a new psychometric scale consisting of a several dichotomous items taken from a larger item bank. The p values (item means) are known. Now I need to calculate the expected mean and ...
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1answer
26 views

Average of values, their standard deviations and ranges

After reading for hours, I am still swimming. I have a set of plasma concentration results from different labs: ...
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1answer
20 views

Coefficient of variation for a subset

How do I calculate the coefficient of variation, CV (or Relative Standard Deviation, RSD) for a subset? e.g. ...
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22 views

Descriptive and Inferential Statistics

I am doing a time series analysis (stock market returns) and I am currently looking at the summary stats. I know the definitions of the individual stats but the one I am stuck on is the relationship ...
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1answer
18 views

Calculating Mean and Standard Deviation From Frequency Chart

I have only a frequency table like that below. How can I get the mean and standard deviation? ...
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3answers
957 views

Roll a 6-sided die until the total $\geq M$. Mean amount by which $M$ is exceeded?

Here is the question: You roll a fair 6-sided dice iteratively until the sum of the dice rolls is greater than or equal to M. What is the mean and standard deviation of the sum minus M when M=300? ...
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21 views

Error bars on graph, skewed data, negative standard deviation

I have only had basic stats. I conducted some research where I have four different treatments and results for the data range from 0-6. I don't need any elaborate stats test, I just want to know how I ...
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0answers
19 views

Where does this formula for calculating pooled standard deviation for calculating Cohen's d come from?

On this page, it is said that the pooled standard deviation for calculating Cohen's $d$ can be calculated as $\displaystyle SD_{pooled} = \sqrt{\frac{SD_{1}^{2}+SD_{2}^{2}}{2}}$. Where does this ...
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11 views

question about deviation and error %

I was conducting an experiment where an indicated temperature on a sensor read -0.2 degree C. But the same temperature on a thermometer read 0.0 degree C. The deviation is equal to 0.2. And the error ...
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1answer
31 views

Development of standard deviation

I have a cloud of (x,y) variables which show two tendencies. They appear linear. As x increases, the y values become more spread out. Using linear regression, I can plot a nice line through them ...
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1answer
15 views

How do I calculate PERT stddev if I use custom weight factors?

According to (for example) http://tynerblain.com/blog/2006/04/13/foundation-series-basic-pert-estimate-tutorial/, the PERT mean estimate is $$\text{meanA}=(\text{optimistic}\ +\ 4 \times ...
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0answers
12 views

Comparing two values in a normal distribution after cutting off the tail of the distribution

I'm doing a sports-related analysis about comparing regular-season performance versus playoff performance, in particular which teams tend to do better during the playoffs. Thus, I'm making a "regular ...
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1answer
37 views

How to compare means, variances and standard deviations of durations for statistical significance

I am trying to compare multiple mean values, variance and standard deviation values for statistical significance. For example I have the following data: Data 1 Mean: 0.01304 Sample ...
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2answers
47 views

Is recoding a categorical variable into a continuous variable possible?

I'm trying to see if it's possible to recode a categorical variable into a continuous variable. The data would probably not permit it but what if I really needed to find the mean and SD? Is there ...
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1answer
38 views

Interpreting standard deviation for PCA

I'm running PCA on my dataset using r and need some help interpreting the standard deviation results. Here are the results ...
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0answers
9 views

Likert scale analysis , how to analyze it in this case?

I have a questionnaire divided in 4 section. Each section has 5 question ; all of the questions are using the likert scale of 7 points (strongly agree, agree..etc..) I want to compare the 4 ...
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0answers
27 views

What is the commonly used mehtod for measuring variance of accuracy mean using k-fold cross validation?

I know there are planty of questions about standard deviation, though I didn't find an answer tuned to my particular need and also I could really use your help! I'm performing 18-Fold Cross ...
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0answers
44 views

Distribution ratio of $\bar{y}$ and $S_x$ when $X$ and $Y$ are correlated normally distributed

If we have two correlated $X\sim N(\mu_2,\sigma^2_2)$ and $Y\sim N(\mu_1,\sigma^2_1)$ with correlation $\rho$, then $\bar{y}$ has $N(\mu_1,\frac{\sigma^2_1}n)$ and $S_x$ follows ...
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0answers
10 views

Combining Standard Deviation (combined measurement uncertainty)

Im trying to figure out the combined SD of two set of data. I am working with Mass data and % iron. Each set has its on SD and i want to determine the Mass of the iron +- ?. Example: Mass = 50 ± X ...
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1answer
42 views

Mean vs. Standard deviation for data ranging between 0 and 1

If e.g. 100 people can rate a subject between 0 and 1 than the dispersion (e.g. standard deviation) among the 100 raters is potentially largest for a mean of 0.5 (50 people rate 0, 50 people rate 1) ...
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1answer
15 views

percentiles of deviation

Disclaimer - I am an amateur and self taught in stats so I apologize if the answer is painstakingly obvious. From what I've read, the average can sometimes hide data regarding extreme values and that ...
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26 views

How to calculate probability of bankruptcy for $E>0$ and given $\sigma$?

I will demonstrate the problem with the simple example. Suppose I want to start a casino. The probability theory tells me that the expected value for my games is greater than zero ($E>0$), and ...
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4answers
97 views

Standard deviation vs standard error of the mean for intervals

I couldn't find a question like this anywhere on Cross Validated. Also I struggled to write the title for this question. Imagine I have a satellite picture of a straight road, and I expect that the ...
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1answer
22 views

SPSS computing pairwise comparisons after repeated measures ANCOVA, standard deviation question

I am reporting standard deviations for pairwise comparisons of adjusted marginal means. SPSS gives me the standard error that I can convert, but I am unsure if SPSS uses the equivalent of N or N-1 to ...
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1answer
27 views

Finding an accurate average with the least number of samples

For the process I am testing, if I run 1000 trials I get an average score of 84.2 with a standard deviation of 11.35. So my question is, is it possible to run this less than 1000 times and still get ...
2
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1answer
20 views

Need calculate and update iteratively Standard deviation

I have a list of Double Values(List of distances form a fixed central point), and I repeatedly chuck out some values(based on simple rule of largest value) and see the change in SD. I would like to ...
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1answer
30 views

Standard deviation visualization for different time series

I want to visualize the following data in the more concise way possible (only 1 figure of possible!) I have the following averaged and std (grey shaded) profiles, which come from 20 different ...
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1answer
60 views

Standard Deviation vs. Standard Error of the mean [closed]

In a medical drug test, which one is reasonable to report along with mean to summarize the variance? SD or SEM?
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1answer
39 views

Standardizing sample factor scores: population or standard deviation

Please note: This question pertains to Q Methodology, a research method used to study people's subjectivity. Q embodies ontological and epistemological assumptions that sometimes differ markedly from ...
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3answers
82 views

Standard error of a population

I measure the weight of 100 people and pick 20 lots of 5 people from these 100. Therefore n = 5, repeated 20 times. The 100 people represent the population and groups of 5 people represent samples ...
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2answers
27 views

How should I determine an average from a set of averages

I have a set of lines. I measure their length each 5 times, and then take the mean of their lengths (as I measure them). I also take the standard deviation. I want to know the 'average' line length. ...
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1answer
62 views

Standard Deviation of small population (less than 30)

Do we calculate the Standard Deviation of a population the same no matter how small (say less than 30) population size gets? Does distribution type play any roles in this? Thank you in advance
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2answers
14 views

Methods for compiler benchmarking?

In computer science, statistical knowledge is quite low in general. You rarely see standard deviation in papers. Now I am trying to improve at least my skills, but I find myself utterly confused about ...
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2answers
81 views

Why is the standard deviation defined using differences^2 instead of differences^4? [duplicate]

I've read some post about why to take the std. deviation and its benefits, here's one of them: Why square the difference instead of taking the absolute value in standard deviation?, and another by ...
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1answer
38 views

standard deviation VS variance

Problem statment: What is the different between standard deviation and variance? What context should it be used for both of them?
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39 views

Confidence intervals for sample mean when estimated standard deviation is 0

I ran a Monte Carlo simulation to determine a confidence interval for the population mean based on N trials. The underlying distribution of results is not normal (the values are discrete -- 0, .5 or ...
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0answers
13 views

Question about relative percent error with widely varying expected values

I'm looking at a large collection of values. These values follow an exponential distribution. I have their probabilities and a pre-made Excel spreadsheet that will auto calculate expected values from ...
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1answer
48 views

Question about probability of 0.99 that an average lies less than L years above overall mean

The duration of Alzheimer’s disease, from the onset of symptoms until death, ranges from 3 to 20 years, with a mean of 8 years and a standard deviation of 4 years. The administrator of a large medical ...
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30 views

Usage of standard deviation in random forests regression (for expected improvement)

It seems to me that the awareness of this problem is not high enough. Often the standard deviation (so the sd from each prediction of each tree in the forest) from the random forest regression is ...
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35 views

Standard error/deviation of the coefficients in OLS

In OLS, the variance of the regression coefficients are computed as $$ \mathrm{Var}(\hat{\beta}) = \sigma^2(\mathbf{X}^\mathrm{T}\mathbf{X})^{-1}. $$ Now, if I need to compute the standard ...
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1answer
23 views

Meaning of confidence interval refered to standard deviation

I was reading a proteomic paper few days ago and I got confused on one aspect. In the paper is written: "The global mean and S.D. of protein ratios (47-1/D3) were calculated for each replicate. The ...
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29 views

Transformation of means and sd in meta-analysis

I am doing a meta-analysis based on the means and standard deviations collected from many other studies. The distribution of the data indicated that I need to transform the data. However, the authors ...
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1answer
26 views

Standard Deviation in Transformation vs annualizing monthly returns?

I'm very confused about this difference, and I wanted to know the reason behind it (If this is very rudimentary, I'm sorry but I can't seem to wrap my head around it). If you were to transform a data ...
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12 views

Standard deviation of squared sample correlation coefficient

Suppose I have two vectors of samples from Bernoulli random variables and I would like to compute (at least approximately) the standard deviation of the estimated Squared Pearson correlation ...
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0answers
29 views

How do I correctly calculate the average and standard deviation of three samples with varying number of data points?

An example: I have three data sets, measured in triplicate: 1, 4, 3, 2, 4, 3 4, 5, 3, 6 6, 4, 3, 5, 7 I want to take the average and standard deviation of the ...
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1answer
66 views

Standard Deviation: Actual values vs Actual Values as a percentage of a total

I think this is an easy one but I'm unfortunately a bit stumped. In short, why are standard deviations of actual values different than the standard deviations of those values expressed as a ...
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1answer
92 views

Calculating mean and variance of normal distribution restricted to interval

If one set a lower and an upper limit on the normal density, is it statistically valid to calculate the mean and Standard deviation of that normal variate. If yes, how can we do that in R? In a more ...