Tagged Questions

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
9 views

How do I determine sample size to validate a requirement when I have a lot of margin?

I apologize if a similar question has been asked, but my search has yielded no results. I am having some trouble nailing down the correct methodology to use to design an experiment I am working on. ...
0
votes
0answers
23 views

Calculate Sample Size with VERY small standard deviation

I am facing a problem trying to estimate sample size for an A/B website test I am currently running trying to investigate difference in revenue per click per day (RPVD). Unfortunately, this metric ...
-5
votes
0answers
30 views

two question about statistic [closed]

An elementary school discipline team is going to set a policy - students who score two or more standard deviations above the mean on a behavior problem scale will be placed into an intervention ...
1
vote
0answers
24 views

When comparing variability between unequal samples, is there a way to correct for sample size?

I am trying to compare test measurements taken at three time points in a training paradigm. The data for each test consists of a number of durations in ms. The variable I'm interested in is the ...
0
votes
0answers
18 views

Cannot intuitively grasp “Standard normal deviate”

I cannot intuitively grasp the meaning of "Standard normal deviates". I think It would help if you provided me with either/all of the following: (i) real life examples of their application, (ii) an ...
8
votes
1answer
195 views

Can we use leave one out mean and standard deviation to reveal the outliers?

Suppose I have normally distributed data. For each element of the data I want to check how many SDs it is away from the mean. There might be an outlier in the data (likely only one, but might be also ...
0
votes
0answers
24 views

nls standard deviation calculation

I have fitted a non linear assymptotic equation to a set of data and my interest is in getting the standard deviations of the fitted parameters. Is this possible in nls?
0
votes
0answers
15 views

how to create such Z-score chart

I have a Z-score chart but I don't know how to create a similar chart. How can I create such Z-score chart?
1
vote
0answers
55 views

Why is permutation test wrong with variance but correct with standard deviation?

I am trying to understand the limits of permutation testing. I wrote up a small permutation test example in R, and found that permutation testing seems to fail when using absolute difference in ...
0
votes
0answers
18 views

Compare 2 RMSE with different Standard Deviation

How can I compare RMSE of two models with different SD. for example I have two models 1) RMSE=3.5 , SD=6.58, and 2) RMSE=17 , SD=28, how can compare these models. thanks
1
vote
2answers
44 views

Is it possible to manually calculate standard deviation for a multiply-imputed survey variable based on the standard error (SE)?

I am analyzing a multiply-imputed complex sample survey data using Stata. For normally distributed numerical variables I want to report the mean and standard deviation. However, the Stata command for ...
1
vote
1answer
31 views

Cumulative standard deviation of variables with different distribution

Suppose we have a set of basketball players, each of which have 9 associated performance categories. Each of these categories has a different distribution. I want to find a good way to represent how ...
0
votes
3answers
40 views

Distribution of the average of a sample of standard deviations

I have a sample of standard deviations. How is its average distributed? The sample is not big so normality is hardly possible. A.B.
1
vote
0answers
27 views

Standard Deviation and Variance

Can someone help me with this question because I'm not sure of how to do it exactly: There are two routes for a worker to get to his office. Both the routes involve hold ups due to traffic ...
1
vote
0answers
71 views

Badidas and Nikit Shoes

Good day everyone, I am self studying statistics at home and in the office whenever i have time. I want to improve my reporting. So i just came across this website and decided to try if could ask a ...
2
votes
0answers
23 views

How do I use the data from a full sample to inform my estimates about a subgroup?

Consider a sample of size $N$ with various observed characteristics: for example, gender and blood pressure. For the overall sample we have the average $\mu$ and standard deviation $\sigma$ of blood ...
1
vote
1answer
118 views

Comparing Standard Deviations with Different Units

Given: the standard deviation is 15.5 cents per gallon in one set of quoted prices and a standard deviation of $5.5 per barrel in another set of quoted prices. There are 33.5 gallons in 1 barrel. ...
0
votes
1answer
51 views

Using Bootstrap to estimate confidence interval of the standard deviation

I am trying to compare two different methods of estimating confidence intervals: a parametric approach that uses the assumption that the sample is t-distributed (i.e. the formulas that are given here: ...
0
votes
0answers
24 views

Bell curve for a table

I have a table in MS-Excel which has cost, product, quartile and Person-days as attributes among others. I have to represent that data in a "nice looking" bell curve or something similar. I haven't ...
0
votes
0answers
19 views

Standard Deviation expressed in percentage

I did an estimation. I got the result, lets call it x. Then, I did the experiment. I got another result, y. I need to know what difference in percentage is between those 2 results? What is the error ...
0
votes
0answers
81 views

Estimating the uncertainty of a bias and a scatter

I have one single set of observational data. Assuming I know the right answer for one property of this data set and then I use one tool to measure this quantity. To get an estimate of the amount of ...
1
vote
2answers
70 views

Adding two (or more) means and calculating the new standard deviation

There are a load of discussions online about adding means and recalculating the standard deviation, but on none have I found answer to this question. I have two sub groups with mean $x_1$ and $x_2$, ...
4
votes
2answers
102 views

How can I work out the standard deviation of a t-distribution?

Given a t-distribution with a certain degrees of freedom, how can I work out what the standard deviation of that distribution is?
2
votes
1answer
26 views

Sampling under assumption of log normal distributed data with sample mean and standard deviation

I have the sample mean and the sample standard deviation of income calculated from individual tax data of all citizens in country (let's call this data X). I do not have access to this tax income ...
1
vote
0answers
39 views

Calculating Standard Deviation of Lognormal Returns with Partial Information

I’m using a stock market portfolio simulation program that unfortunately only provides annualized standard deviation and CAGR (compounded annual growth rate) for the simulated strategy. I would like ...
0
votes
0answers
27 views

Snow tire tread problem

A local tire dealer wants to offer a refunds without taking too big of a risk. The dealer is willing to refund no more than 4% of customers for what mileage can he guarantee these tires to last? The ...
0
votes
0answers
11 views

How to compare the volatility of quarterly p&l of two firms in the same sector?

I want to compare the volatility of the historical quarterly profit and loss (p&l) data of two or more firms operating in the same sector and determine whether the volatility of p&l of these ...
5
votes
1answer
206 views

Why don't we use the unbiased sample variance to calculate the standard error?

The standard error is an approximation of the standard deviation of the sampling distribution of the sample means. The real standard deviation of the sampling distribution, $\sigma _{\bar x}$ is: ...
-1
votes
1answer
29 views

Can Coefficient of Variation be used to verify the representativeness of the mean?

I have a sample with approximately 45 million elements, with 4,410 as the mean and 1,657 as the standard deviation. I am not confident whether or not the mean well represents the sample due to the ...
1
vote
0answers
9 views

How to calculate MoE for subsamples

I have demographic and income data for 3 million people from the American Community Survey (courtesy of IPUMS), and my goal is calculate the median income for every permutation of age group, gender, ...
1
vote
1answer
61 views

Can I use z-scores in right skewed distributions?

I have a right-skewed distribution that represents that number of "likes" on a certain car category for a number of users. What I am trying to do is a sort of classification based on z-scores. For ...
7
votes
2answers
159 views

Why is the standard deviation defined as sqrt of the variance and not as the sqrt of sum of squares over N?

Today I taught an introductory class of statistics and a student came up to me with a question, which I rephrase here as: "Why is the standard deviation defined as sqrt of variance and not as the sqrt ...
0
votes
1answer
33 views

Variance and asymmetry on relative frequency class distribution

I don't know how to resolve this (easy) exercise. I've calculated the first output. But I don't know if it's correct. Calculate arithmetic mean, variance (standard deviation^2), concentration and ...
1
vote
1answer
25 views

Percentage with Normal Distribution

Based on the picture below, there is a value with a percentage that is 68 and 95 percent in relation to standard deviations in a normal distribution. My question is: What do the 68 and 95 percentages ...
0
votes
1answer
65 views

Homework problem. What is the answer supposed to look like?

I am taking a statistics course this semester, and this is part of our first homework assignment, only I don't know what the answer is even supposed to look like. When the process is functioning ...
0
votes
0answers
12 views

real time object tracking

I have correlation value of object using mean and standard deviation, now i want to normalized that correlation value. how can get normalized correlation in terms of percentage vale?
3
votes
2answers
60 views

How to express “inequality” of a distribution in one number

I've got an educational game in the works that challenges players to redraw U.S. state borders in a way that reduce the inequality between big-population and small-population states. As they play, ...
0
votes
0answers
11 views

Assign attributes / categories to users based on their activity / likes

I have a very practical classification problem for which I need some help. I have a database of users along with their activity / likes for a number of car models. I also have the category each of ...
5
votes
2answers
207 views

Average and standard deviation of timestamps (time wraps around at midnight)

I have lots of sensor data with timestamps like "2014-09-09 16:10:45" and accompanying sensor readings. To get some insight into these I want to find "unusual" events by looking at the average and ...
0
votes
0answers
31 views

Maximizing pH values based on mean

It is required to maintain the pH of the water at 7.5 plus or minus .5 in a water treatment process. Two methods of treatment are available. Method 1 gives a mean pH of 7.5 and standard deviation 1.0, ...
0
votes
1answer
34 views

Is comparing standard deviation a valid way to evaluate the usefulness of a sample?

I have data for about 1,800 email messages, and am building a tool in Excel that enables my team to create "benchmarks" on-the-fly -- they can select various characteristics of a message (for example, ...
1
vote
1answer
65 views

cross tabulation of two variables with resulting average and SD

I am beginner of R software. I am looking for two variables and result cross tabulated but not in the form of frequencies. Could I get help on how to get result as average and standard deviation ...
3
votes
1answer
56 views

True standard deviation (hypothesis testing)

I took two statistics classes at college and I remember "hypothesis testing" to be a very powerful tool if only I could apply it correctly. It seems that while I was in college solving problems, I was ...
1
vote
0answers
60 views

Proper use of the coefficient of variation

I have a variety of samples, each with a different standard deviation and mean. The coefficient of variation $CV$ = ${\sigma} / {\mu}$ defines the amount of variation in a population or sample around ...
0
votes
0answers
13 views

Standardizing unbalanced repeated measures data

I have a dataset of height and weight measurements for adult patients in hospital clinic and want to calculate a standardized measure of boy mass index (BMI). For a given pair of measurements, it is ...
0
votes
0answers
18 views

Nested Standard Deviations

This is a finance question but most of it is statistics related. A few years ago the Chicago Board Options Exchange created the volatility index VIX, which is really just the 30-day standard ...
4
votes
3answers
72 views

Analytic or sample standard deviation with binomial data

I've been looking for recommendations on whether it's better to use the sample standard deviation (SD) for a binomial distribution or use the analytic SD (or variance). It's for experiments with ...
0
votes
0answers
23 views

Showing deviation of data on a fixed scale

I'm creating a chart in D3 which shows the Mode from a large (1mil +) dataset; and colors it according to the standard deviation of the dataset. But the issue is that I need to map the range (Red ...
0
votes
1answer
94 views

High Standard Deviation for Leave one out cross-validation?

I am using the leave one out cross-validation technique to evaluate my model. If the prediction on the test sample is right the output is 1 otherwise 0. So I have a array of N samples with 0's and 1's ...
2
votes
1answer
59 views

Standard Deviation After Subtracting One Mean From Another

I've got two sets of data from some fluorescent cells. The first set is when the cells don't have their fluorescence switched on, but they are still faintly glowing. The second set is when they do ...