# Tagged Questions

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.

2answers
27 views

### standard deviation of a certain distribution

If I have a list of N outcomes of drawing a number from the set {-1\$,+1\$}, and I know that the probability of getting (in a single draw) (-1\\$) is p, and probability of getting (in a single draw) ...
2answers
32 views

### to calculate standard deviation using mean and sample size

Given the mean as 1336 and sample size as 24, how to calculate standard deviation when the deviation scores and sample figures are unknown.
0answers
16 views

### Do data points outside standard deviation persist in data subsets?

I have a data set of dates and values that are being plotted. I create a simple trend line y=a+bx using linear regression, and then I create a 'trend channel' (I ...
2answers
32 views

### Quadratic and geometric average

I'd like to find the find the quadratic average and the geometric average. To do this I have these informations : The standart deviation, the arithmetic average and the number of values. I know the ...
1answer
45 views

### Merging standard deviation of two groups with duplicates

I am using Parallel Algorithm (http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Parallel_algorithm) to merge standard deviation of two groups Can we merge two groups if there are ...
0answers
18 views

### Underlying assumption of t-test and standard error

I am having a hard time explaining why my significance test based on randomization is different from a t-test. I have 20 different data points and I know each comes from a Gaussian distribution. I ...
1answer
24 views

### How can I mathematically show the similarity between these 3 plots?

I have 3 3D plots of field strength measured around an antenna. I want to calculate the mathematical similarity between the points of the field patterns. How can I do this? thanks
2answers
44 views

### Can a Covariance matrix have negative elements?

I have a $N \times N$ covariance matrix $C$ of a multivariate Normal distribution. Can any of the elements of the Covariance matrix $C$ be negative for a real-valued distributions ?
2answers
55 views

### Recursive formula for variance

I'd like to know how I can recursively (edit: iteratively) compute variance, so that I may calculate the standard deviation of a very large dataset in javascript. The input is a sorted array of ...
1answer
53 views

### Standard error and p-values

I am a scientist who is currently doing a BSc. I did some stats a few years ago but since haven't touched it. I'm not sure how to calculate p-values for my data. A bit of background is that I am ...
1answer
32 views

### Finding a percentile in Excel

I am writing a program using excel and I need to find the percentage of a number. I have a few sample numbers and their percentages. 2.3% - 5.013368 5.0% - 5.238858 10.0% - 5.480078 25.0% - ...
0answers
14 views

### Remove an observation from an standard deviation

I'm calculating the standard deviation in a iterative manner (due to technical restrictions were recalculating the standard deviation obtaining all the observations has a high cost). A formula to ...
0answers
25 views

### optimum weights for minimum variance

If $X_i$ is an estimator for $x_i$, and an estimate of the sum i.e. $Y = x_1 + x_2 + ... + x_n$ is made by the ration $X_i / p_i$ where $p_i$ is the probability that $X_i$ is chosen , then what are ...
0answers
17 views

### selection for variance reduction in monte-carlo

I need to prove that the following variance reduction operations lead to the optimum value. A related question i asked here about variance reduction gives the optimal proportions are according to ...
1answer
33 views

### variance reduction

Say i have $n$ variables with variances $V_1,V_2,...V_n$. The sum of the variables will have a variance of $V=V_1+V_2+..V_n$ .Now if i am given N total simulations to reduce the variance V, how do i ...
0answers
18 views

### Comparing data to find the “consistently lowest” subset of data.

I am currently faced with a set of data representing the time taken to move and click on an object, in relation to the distance and size of the object (see Fitts's Law if curious but that's ...
2answers
57 views

### Probability of being within one standard deviation of mean given only a moment generating function

I am trying to figure out how to approach this: For starters, I calculated M'(0) and M"(0), which allowed me to find the mean and variance. I got 2 for the mean and 1.6 for the variance. But now, ...
1answer
26 views

### Variance of a sum of correlated variables.

http://www.maths.qmul.ac.uk/~ob/MTH6121/moddocs/chap1_4.pdf I'm currently reading over some notes, linked above, and I've come across a difficulty with proposition 1.27(page 12). Underneath, it says ...
1answer
22 views

### Standard deviation formula

I'm having a lot of doubt on the formula of the standard deviation (in linear regression). My teacher and my syllabus say it's (for $\sigma_x$):  \sigma_x = \sqrt{\dfrac{\displaystyle\sum ...
1answer
46 views

### Statistics Question: Fixed revenue, variable costs

Given a distribution of costs per customer, with a fixed revenue per customer, how would I work out what the profit would be on: mean cost: $\$3.00$standard deviation cost:$\$2.00$ revenue: ...
1answer
26 views

### Is there a better measure of variation for fractional numbers than standard deviation?

For a task I need to do, I'm finding the variance / standard deviation of a set of numbers that are between 0 and 1. When I square the difference from the mean, the square will make the difference ...
0answers
45 views

### Casino Statistics

I am writing an article on european roulette and I was wondering how much do the owners need to put into the pot in relation to the maximum bet allowed on the table to be able to pay out every ...
1answer
30 views

### Find standard deviation given standard deviation

How would I find the standard deviation of a value, V that is the average of other values, say heights of people, given that I have the standard deviation of the heights? I'm looking to improve my ...
1answer
27 views

### Calculating the standard deviation of the sum of a series of randomly distributed variables

Say I roll a six-sided dice 100,000 times. I know that the resulting sums will be normally distributed around a mean of 3.5 How would one go about calculating the standard deviation of the ...
1answer
73 views

### If three groups of unequal sizes have the same standard deviation but different means, will the SD of the pooled data be the same?

Will the standard deviation of all data in three unequally-sized groups each with different means be the same if each group has the same standard deviation? For example, I have a data set as follows: ...
3answers
142 views

### 7.7 standard deviations away from the mean?

I'm confused. I have a problem where I have to find the probability that x is below the z value 7.7. My z table only goes to z values of 3.4. How do I calculate this? These are the hints my teacher ...
0answers
76 views

### Standard deviation of the weighted mean

How do you find the standard deviation of the weighted mean? The weighted mean is defined: $\bar{x} = \frac{\sum{wx}}{\sum{w}}$ The weighted standard deviation (since it is not specified, I take it ...
1answer
565 views

### How to calculate standard deviation and use three-sigma rule for couple variables?

Generally, I have the following data: CampaingOne 49% CampaingTwo 41% I need to use the three-sigma rule and check if the second value is in the interval [- 2 ...
0answers
45 views

### How does standard deviation depend on data?

I've got a problem: I take a random variable, assign values to it and than I have to invent two different probability distribution functions with similar mean values (+-5%), but in the second function ...
0answers
45 views

### What is the purpose of subtracting the mean from data when standardizing?

What is the purpose of subtracting the mean from data when standardizing? and What is the purpose of dividing by the standard deviation?
1answer
197 views

### finding n value basic statistics

I have some practice homework questions. I did the first one I will go over the steps please tell me If I am doing it right. a) As mentioned earlier, it is claimed that 70% of households in Ontario ...
0answers
23 views

### Error rate, one main data set compared to test data set

I have conducted tests where I try to improve the latency for different indepentent scenarios. I have one set a data with values for a year and another set of data for my test period. The ...
1answer
161 views

### How to calculate standard deviation for a series containing both positive and negative numbers?

I got a stream of numbers in one of my apps to represent an electrical signal. I've observed that the signal ranges from -100 to +100. Other than that, the signal is fairly random and crosses 0 in ...
1answer
78 views

### Finding the standard deviation of a set of angles.

My question is given a set of angles in the form of degrees minutes and seconds once finding the mean how do you find the standard deviation. I know how to find the average or mean of a set (see ...
2answers
107 views

### How to vary increase of x as n increments through the Fibonacci series?

Excuse my incorrect use of terminology, I hope my question is clear: I am coding a Python module which tests whether a given number is a member of the Fibonacci series. No problem with that. ...
0answers
45 views

### Compute a separate, running, weighted standard deviation for above and below the mean?

I'll get right to the problem. I have a data set that may or may not be skewed. To account for this, I want to keep track of the variance above the mean and below the mean. I am unable to store the ...
2answers
73 views

### Compare Standard Deviation

The Obama vacations have cost an average of 4 million and a standard deviation of 5 million. The Bush vacations have cost an average of 3 million and a standard deviation of 2 million. What is more ...
1answer
43 views

### Standard Deviation and Variance

Since the start of the Obama presidency, the average number of minutes playing golf each week is 160 minutes and the standard deviation is 20 minutes. The average number of minutes attending cabinet ...
1answer
75 views

### Weighted Standard Deviation for Histogram Bin Height

I'm plotting some binned data in the form of a histogram. Say I have 10 data points, each composed of a bin to be placed in, and then a "height". Then I might have something like: Bin Height 0 - ...
1answer
62 views

### Statistics Question: Revenue & Cost

Data for costs of production for a firm every month from January 2001 to December 2002. Data is denoted by $d_1, d_2,...,d_{24}$. The following info is calculated from the data set. Mean cost = ...
1answer
222 views

### Uniform distribution, Expected value and standard deviation for proportion of observations in a subintervall

$X\sim U(0,1)$. Divide the interval [0,1] into k equal subintervals. Then $X_1$=the number of observtions on the first interval. Define the new variable $Y_1=X_1/n$, where n is the number of ...
0answers
96 views

### Precision of estimated parameter using standard deviation

Consider a set of samples $S$ containing measured samples. From this set, a series of values indicating pressure are derived. Now, a variable X is estimated by taking the maximum value of all the ...
3answers
118 views

### Simple standard deviation question using stocks as example

The following table is from page 171 of Fundamentals of Investing (11th edition) by Gitman, Joehnk, Smart. Please consider only the X, Y and XY columns (second, third, fifth). Portfolio XY comprises ...
1answer
40 views

### Distribution of proportions of each row cell

I'm trying to make sense of some data I have. Below is a simplified version of how data is structured. To get some context, the table shows the distribution of an investor's investments across ...
2answers
182 views

### Advantage of Relative Standard Deviation (RSD)

The definition of RSD is given below: Relative Standard Deviation: In probability theory and statistics, the relative standard deviation (RSD or %RSD) is the absolute value of the coefficient ...
1answer
44 views

### How to average numbers with high standard deviation

I have a set of n numbers that I need to review and come up with the closet average. The set of numbers may or may not have a high standard deviation. Below is an example... Set of numbers.. ...
1answer
62 views

### What is the probability that the 2002 mean salary of a random sample of 50 baseball players was within \$20,000 of the population mean, μ .

Let μ be the mean annual salary of Major League Baseball players for 2002. Assume that the standard deviation of the salaries of these players is \$107,000. What is the probability that the 2002 mean ...
1answer
42 views

### Calculating $P(X-E(X)\geq \mathrm{SD})$ for a normal random variable $X$

If you'd have to calculate the following probability of an $X\sim \mathrm{Normal}$: $$P(X-E(X)\geq \mathrm{SD}),$$ how would you calculate it? And if the calculation will be for $4\cdot\mathrm{SD}$, ...
1answer
898 views

### What is difference between standard deviation and Z-score?

I have read several explanations of standard deviation and z-score, I know how to it calculate them but I am not sure what is differences betwen them. Can someone explain it to me? When is suitable ...
1answer
168 views

### Percentile for a Given Z-Score

Disclaimer: Statistical math person I am not... I'm a programmer that has been tasked with finding the percentile a child will fall in depending on their weight and age according to the CDC. The ...
{"extraction_info": {"found_math": true, "script_math_tex": 0, "script_math_asciimath": 0, "math_annotations": 0, "math_alttext": 0, "mathml": 0, "mathjax_tag": 0, "mathjax_inline_tex": 28, "mathjax_display_tex": 1, "mathjax_asciimath": 0, "img_math": 0, "codecogs_latex": 0, "wp_latex": 0, "mimetex.cgi": 0, "/images/math/codecogs": 0, "mathtex.cgi": 0}, "config": {"markdown_headings": true, "markdown_code": true, "boilerplate_config": {"ratio_threshold": 0.18, "absolute_threshold": 10, "end_threshold": 15, "enable": true}, "remove_buttons": true, "remove_image_figures": true, "remove_link_clusters": true, "table_config": {"min_rows": 2, "min_cols": 3, "format": "github"}, "remove_chinese": true, "remove_edit_buttons": true, "extract_latex": true}, "english_confidence": 0.9162673354148865, "perplexity_flag": "middle"}