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mean standard-deviation standard-error basic-concepts share|improve this question edited Aug 9 '15 at 18:41 gung 74.6k19162312 asked Jul 15 '12 at 10:21 louis xie 413166 4 A quick comment, not an Close Yeah, keep it Undo Close This video is unavailable. You will recall that I asked you to guess which sample you would expect to have the larger standard deviation (#1 or #2). When you gather a sample and calculate the standard deviation of that sample, as the sample grows in size the estimate of the standard deviation gets more and more accurate. news

This can be derived from three properties: The sum of independent random variables is normal, $\mathrm{E}\left[\sum_{i=1}^{n} a_i X_i\right] = \sum_{i=1}^{n} a_i \mathrm{E}\left[ X_i \right]$, If $X_1$ and $X_2$ are independent, $\mathrm{Var}\left(a_1 For example if our variable of interest was height measured in inches then the variance would be reported in squared-inches which makes little sense. Standard Deviation of Sample Mean -1 Under what circomstances the sample standard error is likely to equal population standard deviation? 3 Why do we rely on the standard error? -3 What I would not use means or SD to describe a categorical variable (such as gender or race). navigate to this website

The deviation is calculated by subtracting the mean from each observation. We know in general that $\text{Var}(kY)=k^2 \text{Var}(Y)$, so putting $k=1/n$ we have $$ \text{Var}\left(\frac{\sum_{i=1}^n X_i}{n}\right) = \frac{1}{n^2} \text{Var}\left(\sum_{i=1}^n X_i\right) = \frac{1}{n^2} n\sigma^2 = \frac{\sigma^2}{n} $$ Finally take the square root to To do this, you have available to you a sample of observations $\mathbf{x} = \{x_1, \ldots, x_n \}$ along with some technique to obtain an estimate of $\theta$, $\hat{\theta}(\mathbf{x})$. When the population standard deviation isn't available the sample standard deviation $s$ is used as an estimate, giving $\dfrac{s}{\sqrt{n}}$.

But how accurate is this? There are **other measures** for spread, such as range and variance. Pythagorean Triple Sequence Secret of the universe How could a language that uses a single word extremely often sustain itself? Standard Error Regression The uncertainty in the mean can be used to know how close the average of the samples are to the average that would come from measuring the whole group.

Each chapter describes a different statistical technique, ranging from basic concepts like central tendency and describing...https://books.google.com/books/about/Statistics_in_Plain_English_Third_Editio.html?id=8UpZBwAAQBAJ&utm_source=gb-gplus-shareStatistics in Plain English, Third EditionMy libraryHelpAdvanced Book SearchView eBookGet this book in printRoutledgeAmazon.comBarnes&Noble.comBooks-A-MillionIndieBoundAll sellers»Statistics in March 22, 2012 | Jeremy Taylor Thanks for the useful details Jeremy. share|improve this answer edited Jul 20 '10 at 2:13 answered Jul 19 '10 at 19:35 Baltimark 77911019 6 this is an incredibly unclear response. Also, the relative uncertainty is the uncertainty in the mean divided by the mean, times 100%.

i.e if mean is 3, is 1 low...if so is 1.5 low or high?....etc July 2, 2012 | andreea I would echo earlier postings, you have done a masterful job of Standard Error Of The Mean Definition But also consider that the mean of the sample tends to be closer to the population mean on average.That's critical for understanding the standard error. Loading... Kevin Piers 254 views 10:39 Statistics 101: Standard Error of the Mean - Duration: 32:03.

The table shows weights for two samples of redfish, all 42cm long. http://jeremyjaytaylor.squarespace.com/smmctheblog/confusing-stats-terms-explained-standard-deviation.html The SEM, by definition, is always smaller than the SD. Standard Error Formula Standard error From Wikipedia, the free encyclopedia Jump to: navigation, search For a value that is sampled with an unbiased normally distributed error, the above depicts the proportion of samples that Standard Error Vs Standard Deviation But such an unfocused question on such a basic topic indicates (to me anyway) that the poster didn't even try to find an answer.

This gives the standard deviation. navigate to this website Thanks for any reply-Sean February 11, 2013 | sean I think I would think of SD more as a measure of how much your sample tends to vary from the mean. It takes into **account both** the value of the SD and the sample size. Can you help me out? How To Interpret Standard Error

This is much more intuitive and is therefore more popular than the variance. y <- replicate( 10000, mean( rnorm(n, m, s) ) ) # standard deviation of those means sd(y) # calcuation of theoretical standard error s / sqrt(n) You'll find that those last A case in point is estimating a proportion $p$, where you draw $n$ items each from a Bernouilli distribution. More about the author If I am told a hard percentage and don't get it, should I look elsewhere?

Richard Frederick 5,799 views 9:30 Standard Error of the Mean Compared to Standard Deviation using SPSS - Duration: 7:32. Difference Between Standard Error And Standard Deviation Someone who is "very bright" is two standard deviations above the mean, meaning an IQ test score of 130. link –Vaibhav Garg Feb 6 '12 at 7:10 Yes, I had seen that link before.

Both SD and SEM are in the same units -- the units of the data. Stephanie Glen 24,698 views 3:18 Standard Deviation vs Standard Error - Duration: 3:57. We can then draw in vertical lines which connect each data point to the mean line - these are the deviations of each data point from the mean, and we call Standard Error Calculator The Cambridge Dictionary of Statistics, CUP.

It contains the information on how confident you are about your estimate. The variance of each $X_i$ distribution is $p(1-p)$ and hence the standard error is $\sqrt{p(1-p)/n}$ (the proportion $p$ is estimated using the data). February 11, 2013 | Jeremy Taylor I like this. http://interopix.com/standard-error/standard-error-standard-deviation-divided-by-square-root.php It is a way to know how sure you can be about the average from the sample.

The standard error of the mean estimates the variability between samples whereas the standard deviation measures the variability within a single sample. share|improve this answer answered Jul 22 '10 at 15:36 Freya Harrison 1,93231727 add a comment| up vote 1 down vote If the information required is the distribution of data about the Thank you very much!!! :-) October 2, 2012 | happyaboutstatsnow could you please explain to me how standard deviation in relation to gender works? As you collect more data, you'll assess the SD of the population with more precision.

standard-deviation basic-concepts share|improve this question edited Jul 30 '13 at 10:19 Nick Cox 28.4k35684 asked Jul 19 '10 at 19:27 Oren Hizkiya 406710 21 Is this really the kind of Common measures of centre include the mean, median and mode. Brandon Foltz 70,074 views 32:03 Standard error of the mean - Duration: 4:31. November 20, 2012 | Jeremy Taylor Thank you very well done November 21, 2012 | Rick Ryan Outstanding explanation, keep up the good work bro!

current community blog chat Cross Validated Cross Validated Meta your communities Sign up or log in to customize your list. So, what you could do is bootstrap a standard error through simulation to demonstrate the relationship. We than find the variance of this quantity and get the standard deviation by taking the square root of its variance. Sometimes the terminology around this is a bit thick to get through.

Browse other questions tagged mean standard-deviation standard-error basic-concepts or ask your own question. MrNystrom 592,469 views 17:26 Standard error of the mean and confidence intervals - Duration: 9:30. more stack exchange communities company blog Stack Exchange Inbox Reputation and Badges sign up log in tour help Tour Start here for a quick overview of the site Help Center Detailed April 10, 2013 | Jess Thanks, Jess!

We observe the SD of $n$ iid samples of, say, a Normal distribution. See Terms of Use for details. But to make probability statements you need to know something about the distribution, be it normal, binomial or whatever. Thanks to your simple explanation it is now very clear to me, great.

Pandas - Get feature values which appear in two distinct dataframes What exactly is a "bad," "standard," or "good" annual raise? Dr.

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