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In statistics, the standard deviation (SD, also represented by the lower case Greek letter sigma σ for the population standard deviation or the Latin letter s for the sample standard deviation) is a measure that is used to quantify the amount of variation or dispersion of a set of data values. A low standard deviation indicates that the data points tend to be close to the mean (also called the expected value) of the set, while a high standard deviation indicates that the data points are spread out over a wider range of values.
The standard deviation of a random variable, statistical population, data set, or probability distribution is the square root of its variance. It is algebraically simpler, though in practice less robust, than the average absolute deviation.
A useful property of the standard deviation is that, unlike the variance, it is expressed in the same units as the data.
In addition to expressing the variability of a population, the standard deviation is commonly used to measure confidence in statistical conclusions. For example, the margin of error in polling data is determined by calculating the expected standard deviation in the results if the same poll were to be conducted multiple times. This derivation of a standard deviation is often called the "standard error" of the estimate or "standard error of the mean" when referring to a mean. It is computed as the standard deviation of all the means that would be computed from that population if an infinite number of samples were drawn and a mean for each sample were computed.
The standard deviation of a population and the standard error of a statistic derived from that population (such as the mean) are quite different but related (related by the inverse of the square root of the number of observations). The reported margin of error of a poll is computed from the standard error of the mean (or alternatively from the product of the standard deviation of the population and the inverse of the square root of the sample size, which is the same thing) and is typically about twice the standard deviation—the half-width of a 95 percent confidence interval.
In science, many researchers report the standard deviation of experimental data, and only effects that fall much farther than two standard deviations away from what would have been expected are considered statistically significant—normal random error or variation in the measurements is in this way distinguished from likely genuine effects or associations. The standard deviation is also important in finance, where the standard deviation on the rate of return on an investment is a measure of the volatility of the investment.
When only a sample of data from a population is available, the term standard deviation of the sample or sample standard deviation can refer to either the above-mentioned quantity as applied to those data, or to a modified quantity that is an unbiased estimate of the population standard deviation (the standard deviation of the entire population).
Up for sale is a like new MDT V5 Standard stock in black
Stock was only installed for a day, then removed. Comes with all the hardware.
Asking: $325 obo
Trade option: Atlas Bipod BT46 with Lever/clamp.
Thanks for checking out my listing.
Picatinny rail mount for FAL rifles. This is the carry handle version, Model Number: 620A-A. I never took this out of the original packaging. It is brand new.
PayPal friends and family, Venmo cash app or check/money order.
Free ship by FedEx ground in the Pacific Northwest
Browning Belgium A5 Standard 12 gauge.
Mid 1950's vintage (FN made). 2-3/4".
Some cosmetic blemishes on stock consistent with its age, which I have tried to show, but in good condition and overall a pretty nice and classic semi-automatic shotgun .
Interested in quality .22 pistols/revolvers...
I've got 2K fresh CCI magnum small pistol primers. Willing to trade for standard small pistol or large pistol. I know I can use them so not looking for advice, thanks. Just figured if someone out there needs magnum and can't find them we can help each other out.
Will be traveling up to Portland...
Selling my RIA 1911 Chambered in 45 Auto. new pachmayr rosewood grips (can Include original wooden grips if you want them) Swapped out front iron sight for a fiber optic. Less than 300 rounds through this. Made sure to keep it clean and oiled. Comes with three mags. Asking $425. Willing to...
NEW (takeoff) BCM Standard 14.5 Socom barrel with F height FSB
Pinned F height FSB
I take PayPal friends and family
Shipping OK, S/H free
No separate parts purchase requests please.
No trade requests please.
No face-to-face sales requests please
Like new standard co geronimo iwb holster for surefire x300A/B lights. Basically a universal holster because retention is on the light instead of on the firearm and holster is not encasing the entire firearm so really any handgun will work. New is $75+shipping. Looking for $60. Located in...
I have 3 bricks of CCI standard velocity that I would like to trade for CCI 40grain copper plated minimags, no hollow points. My pistol doesn't like the standard velocity. No premium for the minimags, trade would be even up
Hey, up for sale are 1000 Round Cases - 7.62 x 39 122 Grain FMJ Russian Made Red Army Standard Ammo - AM3092 RAS
- $530 SHIPPED Ground EA. 1000 RD Case OR $500 CASH FTF Vancouver, WA
ZELLE or CashApp - NO COMMENTS PLEASE (DISCREET)
Post I'll take 1 or 2 or however many you'd like.
NEW BCM Standard 14.5" M4 (SOCOM) Upper Receiver Group
Factory complete upper build
M4 Feed Ramp Barrel Extension
Barrel Length:14.5in Barrel
Style: Standard (SOCOM)
F height FSB
No Bolt Carrier Group
Also includes genuine Colt trigger guard for those of you that are...
I have for sale a Microtech Ultratech D/E Distressed Tan Apocalyptic Standard OTF knife for sale. **SOLD**
This knife has seen little pocket time, fires hard and comes with the box and docs.
I’m asking $230 and prefer a face to face sale in SW Portland/Beaverton/Tigard area.
6 boxes of Red Army Standard in 7.62x39. Brass case, 123 gr FMJ. Prefer to sell all 180 rounds together.
Buyer pays any shipping and fees. Can only ship UPS Ground per restrictions. No trades. Thanks for looking.