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.

learn more… | top users | synonyms (2)

0
votes
0answers
28 views

How to find p value range for two sample test given only sample size and standard deviation?

Edit: got access to the data and have sample means. Sorry! Can delete.
0
votes
0answers
9 views

How would I average noisy data representing the noise using error bars?

I have data that was binned in a process that provides the average and standard deviation for the values in each bin. For some of the data, the variation between bins is significantly larger than the ...
0
votes
1answer
17 views

Standard Error for Weighted Values

I want to calculate the standard error for an experimental measurement. The data is stored as a 2D image which is circularly symmetric about a center point. To reduce the data we radially integrate ...
1
vote
0answers
16 views

Can you calculate descriptive statistics (SD, SE particularly) from percentages and ratios?

I'm a cell biologist and a lot of my data is expressed as a fraction (percentage) of the total number of cells in a single experiment in a number of separate categories (generally 5 or so). The number ...
1
vote
0answers
35 views

How can we get “estimated standard deviation” from MLE?

I'm looking for MLE as in the following picture. I have some questions: How can we get "the estimated standard deviation"? Is "the estimated standard deviation" included in the output of the ...
1
vote
0answers
20 views

How can we calculate the standard deviation of multiple values with different uncertainties each?

For example, if I have a set of readings, like: 13.4 +/- 0.5 14.5 +/- 0.7 12.8 +/- 0.6 13.9 +/- 0.4 14.8 +/- 0.5 How do I calculate the standard deviation of ...
1
vote
0answers
13 views

Standard deviation comparison for splitting clusters in ISODATA

I am currently implementing the ISODATA algorithm and I am new to cluster analysis as I just learnt about it. I got stuck at the step which I need to compute the standard deviation of each cluster, ...
0
votes
1answer
35 views

Is my Interpretation of this statistical distribution correct? [closed]

The torque of shld flx action was between 8Nm to 10NM for 10% of the time Is my interpretation correct? If so how do I determine torque for one of the 19 activities?
0
votes
0answers
12 views

calculating error for percent inhibition

I'll apologize in advance for leaving out pertinent information as I'm sure that I will. It has been a long time since I've devoted any time to statistics, so bear with me. I have 2 sample sets, a ...
0
votes
0answers
42 views

threshold based on mean and standard deviation

I have a time series of 70000 data points. I want to separate samples of this time series which have very large values as compared to the time series. How can i threshold sample to separate. What i ...
0
votes
1answer
51 views

Confidence intervals vs. standard deviation

The 95% confidence interval gives you a range. The 2 sigma of a standard deviation also gives you a range of ~95%. Can someone shed some light on how they are different?
0
votes
0answers
35 views

Bounding the bias of standard deviation estimate for stratified sampling (MC)

I cannot find an answer to this issue: in Monte Carlo runs, if one uses stratified sampling then the unknown bias of the variance estimator ( $\bar{\sigma}^2=\frac{1}{N}\sum{(y_i-\bar\mu_y)}$ where ...
0
votes
1answer
19 views

Comparing mean differences between groups when standard deviation in one of them is 0

I was wondering if it is possible and -if yes- what are the implications when one is trying to compare mean group differences of a continuous variable that varies in one group but is a constant number ...
0
votes
0answers
27 views

Median Absolute Deviation vs Standard Deviation

To measure spread we use Variance or Standard Deviation. Variance and hence Standard deviation uses mean to find out the spread. Recently came across the MAD (median absolute deviation). ...
0
votes
0answers
30 views

How to plot mean plus/minus standard deviation for histograms?

I have a set of grayscale images, where the pixels may have values in the range $[0, 255]$. From each image, I calculate a histogram, which shows how many pixels have the value $0$, $1$, $2$, and so ...
0
votes
1answer
18 views

Measuring share contribution of each var/cov term to the standard deviation of a sum of variables

Say, for a simple example, I have a random variable $X = \alpha_1 X_1 + \alpha_2 X_2$, where $X_i$ are random variables and $\alpha_i$ are weights. I then calculate the standard deviation of $X$ as ...
2
votes
1answer
27 views

Evening out a set of buckets

(I am not strong in statistics so please forgive me if I don't use the correct terms here) Let's say I have a book with many (1000+) sections, and each section varies significantly in the number of ...
1
vote
1answer
20 views

Multivariate Standard Deviation

I'm not sure I'm describing this 100% correct, but here goes. Is there a way to find out the overall standard deviation of a data point if it has multiple variables? For example, If I have the ...
1
vote
0answers
52 views

How to calculate mean and standard deviation of a range variable (grades) when the raw data is based on frequency categories?

Results of an exam indicate that: 13% of the class earned an A 20% earned a B 48% earned a C 10% earned a D 9% earned F's The grade C ranges from 70-79%. Assuming that the data is normally ...
2
votes
1answer
67 views

How many samples needed to determine value 4 sigma away from mean?

I have a source that generates computer files varying between 20,000 and 40,000 bytes in length. I think (strongly assume so) that they vary in length according to a Normal distribution. They average ...
0
votes
1answer
45 views

Making the most of Standard Deviation and P value — graphing?

I have a question or two in regard to getting the most out of the statistics of my data. By way of background, my qualitative observations of two distinct populations that are uniformly regarded to be ...
0
votes
1answer
23 views

Random Walk Probability Including Drift

What is the equation for the probability of a random walk with drift being equal to a specific value after n steps, given a specific standard deviation?
0
votes
2answers
15 views

Determining parameters for distribution of standard deviations

I have a database of 10-star movie ratings (similar to IMDB), with a large number of movies and an also large number of ratings for each movie. For each movie I have computed the mean and stddev of ...
0
votes
0answers
30 views

Standard deviation error bars and kruskal.test in R

I need to test if there is a significant difference between two groups of data, each with three replicates. (Multiple groups) I used the following approach: ...
0
votes
1answer
34 views

Distribution of the stddev of movie ratings

I have a database of 10-star movie ratings (similar to IMDB). For each movie the raw data is a distribution of votes from 0-star all the way to 10-star, and I have also computed the mean and standard ...
3
votes
1answer
41 views

Is it correct to use plus or minus symbol before standard deviation?

I have represented standard deviation as "±SD" before in publications. But I like to have opinions on this. Is it appropriate to use the notation '±' with SD ? Or is it only for Standard error ?
1
vote
0answers
36 views

Why is standard-deviation considered to be L2 distance?

I'm trying to really understand what SD is telling me, but the information out there is sparse and confusing. This thread and some others as well provide the answer that SD is L2 distance in ...
0
votes
0answers
13 views

NMSE - division by zero

I am using the normalized mean square error function in the Python Oger Toolbox which is defined as: ...
0
votes
0answers
20 views

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 ...
0
votes
0answers
18 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 ...
0
votes
2answers
42 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 ...
1
vote
1answer
98 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 ...
0
votes
1answer
37 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: ...
0
votes
1answer
23 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. ...
0
votes
0answers
23 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 ...
1
vote
1answer
32 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? ...
9
votes
3answers
1k 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? ...
0
votes
0answers
35 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 ...
0
votes
0answers
21 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 ...
0
votes
0answers
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 ...
1
vote
1answer
35 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 ...
2
votes
1answer
23 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 ...
2
votes
0answers
15 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 ...
1
vote
1answer
47 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 ...
2
votes
2answers
54 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 ...
3
votes
1answer
51 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 ...
0
votes
0answers
13 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 ...
0
votes
0answers
31 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 ...
2
votes
0answers
45 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 ...
2
votes
0answers
14 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 ...