Standard deviation Definition and 271 Threads

Hi, can someone just confirm that to get the GSD of a distribution, I simply take the natural log (or log 10?) of all the numbers then find the arithmetic standard deviation of that? Thanks :)

The mean and standard deviation of a random variable x are -11 and 4 respectively. Find the mean and standard deviation of the given random variables: 1) y=x+7 2) v=8x 3) w=8x+7 2. Homework Equations : E(x) = u, E(ax+b) = aE(x)+b The Attempt at a Solution I've gotten...

Homework Statement It has been projected that the average and standard deviation of the amount of time spent online using the Internet are, respectively, 14 and 17 hours per person per year (approximately normally distributed). What value is exactly 1 standard deviation below the mean?Homework...

Okay... this is a really simple question but I am pratically going nuts over it I can't sleep, I've been looking at it for like 12 hours, googling and wiking over it I am going crazy... Okie... Suppose I have 4 numbers, 0, 2, 4 and 6 and I grab 2 random ones with replacement... so I have...

The uncertainty is interpreted as standard deviation, then does it mean uncertainty principle only has statistical meaning? I mean, is the principle only meaningful when a particle's momentum and position are measured simultaneously by many detectors?

Hello, I seriously need some help as I can't figure out what to do here. I am working on coding a vaccination simulation that measures rates of infection for period of 100 days. I have this variable delta, which is the number of days the infection period lasts. Delta is 5, or at least on...

I am an independent researcher ready to compile data from an experiment. I have a set of measurements that include the uncertainties of measurement. If I calculate the mean for the set (and thus the standard deviation) do I need to include the uncertainties when doing this calculation?

I'm new to studying statistics but it seems to me like standard deviation and kurtosis measure the same thing. The higher the standard deviation, the more spread out the data is, while the lower the kurtosis the more spread out the data is. I'm sure I'm wrong about this so can someone help...

I am a little confused about the justification behind what we do with things we believe to be poisson distributed. Take for instance, gamma-decay counts from a scintillation detector. Suppose we got 100 counts using a 1 minute integration time. We would then assume that the distribution of...

What are the advantages of using the absolute mean deviation over the standard deviation. Is it possible to show a simple example where the former is more (or less) appropriate? Also, related to the mean deviation is my own variation. Does it have a name? Instead of calculating the absolute...

Hello again, I have a question here that asks me to find how large a sample size is, but I have no Standard deviation. How would you tackle this> How large a sample size do we need to estimate the mean annual income of natives in New York, correct to within $1000 with probability 0.99? No...

I am comparing two RMS error time-series and I would like to generate error bars on the RMS results. I think the RMS error is a standard deviation of an assumed zero mean process, and I have the gut feeling that this should be the standard deviation of the sample standard deviation. Is that...

1. An airline's flights have a mean arrival time of 5.8 min late with standard deviation of 2.1 min. What would be the appropriate x - scale for a histogram? 2. http://www.mathsrevision.net/gcse/sdeviation2.gif 3. I tried to do this problem, but I couldn't think of anyway to find...

Homework Statement A health physicist is testing a new detector and places it near a weak radioactive sample. In five separate 10-second intervals, the detector counts the following numbers of radioactive emissions: 16, 21, 13, 12, 15. a) Find the mean and standard deviation (SD) of...

Homework Statement 1) A random sample of 26 students who are enrolled in College A was taken and their SAT scores were recorded. The sample mean is 548 and the sample standard deviation is s=57. Assume population is normally distributed. a) Find a 98% confdience interval for the standard...

Homework Statement Data set in X with mean xbar = 100 and standard deviation Sx = 10 Find ybar and Sy for 2(Yi-5)/10 + 7 Homework Equations The Attempt at a Solution All the problems I have seen are in the form yi = axi + b in which case the mean ybar = a(xbar) + b and...

Homework Statement The resistances of 50 resistors are measured and the results recorded are as follows: Resistance x Frequency 1.) 5 x 17, 2.) 5.5 x 12, 3.) 6 x 10, 4.) 6.5 x 6, 5.) 7 x 5) Calculate standard deviation of the measurements Homework Equations The...

There are two things I don't understand here: Firstly, why in the standard deviation expression we use the Q operator instead of the Q value itself? Writting Q seemed more natural and then in the next expression I would just stick the corresponding operator. Which would lead to the same result...

hello can anyone explain what the difference is between RMSE and standard deviation. I am using RMSE in multivariate analysis but is it just the standard dev. why another name?

What is the formula for standard deviation?

Hey guys, Just a question which has been puzzling me for some time. I am told that means of samples of a population can be normally distributed with mean of \mu and with standard deviation of \sigma/\sqrt{}n Can someone please explain to me how the standard deviation is derived or is it...

Homework Statement The scores on an exam are normally distributed, with a mean of 77 and a standard deviation of 5. What percent of the scores are greater than 87? Homework Equations The Attempt at a Solution I don't understand what it is exactly that I have to do to get the...

Homework Statement Due to the expense involved, car crash tests often use small samples. When 5 BMW cars are crashed under standard conditions, the repair costs (in dollars) are as shown in accompanying list. Use 0.05 significance level to test the claim that the mean for all BMW cars is...

Hello, The standard deviation is calculated as: http://www.mathsrevision.net/gcse/sdeviation2.gif Now the problem I have is that how you calculate the standard deviation (more accurately?) over both samplesvif you have two samples of different size, n1 and n2, in which the level of the...

Homework Statement If there are 4 children in a family, find the probability of getting exactly 3 girls. Find the mean, variance, and standard deviation. Use two different methods(binomial distribution method and general probability distribution method). Homework Equations Binomial...

"Normalizing" standard deviation between two data sets I have a baseline set of data collected which has a standard deviation of X, and then I collected another set of the data under a different condition (different temperature), and this has a different standard deviation Y. How do I cancel...

Hi guys. Im new at this site so please be nice to me =P. I've been working on some practice papers for my upcoming end of semester exams. Cant get these two questions out ><. Any help is greatly appreciated Thanks in advance jenny xoxo 1. A sample of 28 students measured their...

Given the mean energy of a system in a heat bath is \bar{E} = - \frac{\partial ln(Z)}{\partial \beta} Where Z is the partition function and \beta = k_BT Why is the standard deviation of E defined by: (\Delta E)^2 = \frac{\partial^2 ln(Z)}{\partial \beta ^2} I can't seem...

Standard deviation and mean - "combining" the two Lets say one was to have a range of data, with the mean and standard deviations for the different subsets of data. The "best" subset is that with the lowest mean, however how do I include the standard deviation when making my decision. For...

Homework Statement Problem 1.2 from the book Introduction to Quantum Mechanics (2e) by Griffiths: Suppose a rock is dropped off a cliff of height h. As it falls, a million photos are snapped, at random intervals. On each picture the distance the rock has fallen is measured. a) Find the...

This might be embarrasingly easy or impossible; I've been a computer programmer for too long since my statistics classes to tell for sure :blushing: I have a set of records with the following data for each record: interval, mean speed, standard deviation of speed, number of observations...

Hey i was wondering if anyone could help me with this question at all? I don't have a clue about the calculations and would be grateful if it could be explained to me! I'm really struggling! Thanks Some light emitting diodes are tested and a sample is found to have a mean lifetime of 2048...

but only knowing the previous standard deviation, the previous mean (and the sample to be removed). does anyone know how to do it?

In doing a problem, I considered N (a large number, in the range 100,000-1,000,000) raindrops, falling into A (fixed at 100) segments on a roof, distributed using a random number generator I programmed. In considering the number of raindrops that fell into a given segment, the average would be...

[SOLVED] Quick question about finding standard deviation Now I know that \sigma=\sqrt{var(x)} which simplifies to this expression : \sigma=\sqrt{\frac{1}{N}\sum_{i=1}^{N}(x-\overline{x})^2} can someone show me how they got such an expression? and in chemistry I have to use a standard...

Homework Statement For this set of data find the mean and standard deviation Temp...# of days 90-94...1 85-89...3 80-84...6 75-79...12 70-74...7 65-69...1 2. The attempt at a solution I don't know how to find the mean or standard deviation when the data is divided into...

Homework Statement The mean height of players in a basketball competition is 184 cm. If the standard deviation is 5 cm, what percentage of them are likely to be: a) taller than 189 cm b) taller than 179 cm c) between 174 cm and 199 cm d) over 199 cm cm tall? Homework Equations...

Hi all. If I have a function V(x1,x2,x3,x4) and I want to calculate it's standard deviation when x1,x2,x3,x4 are standard normal and their variances are small, then formula (8) on this page http://www.devicelink.com/mem/archive/99/09/003.html" is an approximation to the standard deviation...

For sets X and Y, is it true that s_{XY}=s_{X}\overline{Y}+s_{Y}\overline{X}, where s represents the standard deviation and XY is the set containing x_{i}y_{i}?

Read gambling problem/Standard deviation Posted: May 23, 2007 4:57 AM Click to edit this message... Click to see the message monospaced in plain text Plain Text Click to reply to this topic Reply I'm analyzing some data from online gambling sites.I'm trying to prove they are...

Hi, I was trying to solve this question but my answer is different to the one given by my textbook. "The weight of a randomly chosen plastic washer is normally distributed with mean 5g. Calculate the standard deviation in grams given that the probability that a randomly chosen washer weighs...

Very basic question which has confused me: if the variance of an expectation value <A> is: uncertainty of A=<(A-<A>)^2>^0.5 how is this equal to: (<A^2>-<A>^2)^0.5 ??

I wrote a program that is supposed to find the standard deviation of a set, but something really strange happens in a for loop that I have in my main function. int main() { int i=1; int NUMBER_OF_ELEMENTS; double data[NUMBER_OF_ELEMENTS]; cout << "Please enter the number of...

Standard Deviation Problem in Physics. Help!? Homework Statement In working with Wheatstone bridge one student chose the value for R1 so that the bridge is balanced at L1 = 48.5 cm and L2 = 51.2 cm. If Each measurement has an uncertainty of +/- .05, what would be the minimum value for the...

Homework Statement In a recent survey, 80% of the community favored building a police substation in their neighborhood. If 15 citizen are chosen, what is the standard deviation of the number favoring the substation? Homework Equations I know that my mean is 15 and the probiblilty is 80...

I have a question about standard deviation. If I have a hundred of distance data, how can I use standard deviation to choose a suitble range of the distance. What is the relation between standard deviation graph and my data. I can plot a graph using mean and std of the data, but do not know how...

Exam is in the next 30 mins so please reply ASAP. I just need help with this question. For a sample of size 5, x1 - mean = -5, x2 - mean = 9, x3 - mean = -7, x4 - mean = -2 and x5 - mean = 5 What is standard deviation... answer is 6.782 by squaring all the answers, dividing by n-1 and...

Homework Statement This is my data: 42.4, 65.7, 29.8, 58.7, 52.1, 55.8, 57.0, 68.7, 67.3, 67.3, 54.3, 54.0 I need to find the standard deviation of this list of data. 2. Homework Equations standard deviation= : s^2=\frac{\sum_{i=1}^n(x_i -\overline{x})}{n-1} Actually the standard...

A department store has determined that 25% of all their sales are credit sales. A random sample of 75 sales is selected and the proportion of credit sales in the sample is computed. a) What is the probability that the sample proportion will be greater than 0.34? my answer is: n=75 p=0.25...

Hey all. Im doing maths methods 5 (i live in Australia) and I've run into this problem. A university study investigated the increase in heart rates(measured in beats per minute) of people undertaking a particular exercise. The increases in heart rate were normally distributed with...