Mathematics Stack Exchange
Mathematics Stack Exchange

Questions tagged [standard-deviation]

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. Use this tag alongside (statistics).

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.

1413 questions
0
votes
1 answer

Standard deviation with example problem

Decide "variance" and "standard deviation" for the following material: material I am using the following formula for "variance". $$ s^2 = \frac{1}{n-1} \left( \sum_{i=1}^n x_i^2 - \frac{1}{n}\left(\sum_{i=1}^n x_2 \right)^2 \right) $$ Where √s^2 =…
Sigrid
  • 3
0
votes
1 answer

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 the proof follows from 1.24. I can very easily…
user65132
  • 287
0
votes
1 answer

How can I calculate the potential values of the final value from the value of standard deviation?

If I have a list of 99 values, say $x_1$ to $x_{99}$, and I have a value for the standard deviation of an $x_{1}$ to $x_{100}$ data set, containing these 99 values + 1 other, can I calculate the potential values for the extra data point? Is there a…
user197686
  • 3
0
votes
0 answers

What is the difference between standard deviation and average of absolute difference of any two numbers?

For a set of data $(x_1, \ldots, x_n)$ and its mean $x'$, the standard deviation is calculated by $$ \sqrt{\frac{\sum_i(x_i - x')^2}{n}} $$ , while the absolute difference of any two numbers can be computed by $$ \frac{\sum_i|x_i -…
mallea
  • 829
0
votes
1 answer

Standard Deviation of a distribution

The manager of XYZ shop orders 110 cartridges per week but runs out cartridges every 1 out of 4 weeks. He knows that on average the shop uses 95 cartridges per week. What is the standard deviation of this distribution What i did: $np = 95$ $110(p)…
bryan
  • 147
  • 1
  • 8
0
votes
1 answer

two definition of variance identity

$I_n$ is the indicator rv where $I_n=1$ if $A_n$ occurs and 0 otherwise. Then define $\eta_n = \sum_{k=1}^n I_k$ I'm given this statement: But in another post about the same proof, I have this: $X_n$ is the same r.v. as $\eta_n$ But in the…
user8290579
  • 886
0
votes
1 answer

Standard Deviation of pre/post test scores

I have a problem that I need help with, please! I have results of a pre/post test and I was asked to find the standard deviation for that particular question. Here is what the output looks like: enter image description here 30 users filled out the…
Arthur Farina
  • 11
0
votes
1 answer

Overall standard deviation of two groups without data points?

$15$ boys: mean of $47.6$, standard deviation of $11.2$. $10$ girls: mean of $49.1$, standard deviation of $15.4$. Overall standard deviation of the marks? How would I go about accurately finding the standard deviation from this question? I already…
Austen Clark
  • 3
0
votes
0 answers

Implication of ± 2 standard deviation

I am currently taking a statistics class where we are studying about Standard Deviation. Even though it is a new concept for me still I am able to grasp it fairly quickly. But, we discussed something in the class which I could not understand. The ±2…
Aiguo
  • 101
0
votes
1 answer

Is it mathematically possible to calculate the total standard deviation of a daily list of numbers from their daily rolling standard deviations

Say I have the following list of numbers, each corresponding to a single day: list = [1, 6, 7, 12, 5] I can calculate the daily, rolling standard deviations between each as: stds = [NaN, 3.54, 0.71, 3.54, 4.95] Is it now possible to…
KOB
  • 293
0
votes
1 answer

Calculate Standard Deviation for rolling average

Good morning Math Experts, I am having difficulty figuring out how to calculate the standard deviation for a set of data. Here is the request from my user: Going back three years from today, calculate the yearly average of contacts an officer has…
Leslie
  • 101
0
votes
2 answers

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 unusual: an Obama vacation that costs 5 million…
Shaily
  • 125
0
votes
1 answer

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 meeting per week is 6 minutes and the standard…
Shaily
  • 125
0
votes
0 answers

Find sample standard deviation with mean and mean of their square

I have a problem to find sample standard deviation when only the mean and mean of their square are given. Mean = 19.19 and mean of their square is 618.10 How to calculate sd when there is no N value given here?
Jos Butler
  • 11
0
votes
2 answers

Standard Deviation given n, Σx, Σx²

I have been trying to solve this problem for over half an hour now. I don't know if it is to do with my incapability of using a calculator or a misunderstanding in standard deviation. Question: A sample of 10 people complete a task and their times,…
Karan Bal
  • 13
1 2 3 4 5
6
7 8