In statistics, the standard deviation is a measure of the amount of variation or dispersion of a set of values. A low standard deviation indicates that the values tend to be close to the mean (also called the expected value) of the set, while a high standard deviation indicates that the values are spread out over a wider range.
Standard deviation may be abbreviated SD, and is most commonly represented in mathematical texts and equations by the lower case Greek letter σ (sigma), for the population standard deviation, or the Latin letter s, for the sample standard deviation.
The standard deviation of a random variable, sample, 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 unit as the data.
The standard deviation of a population or sample and the standard error of a statistic (e.g., of the sample mean) are quite different, but related. The sample mean's standard error is the standard deviation of the set of means that would be found by drawing an infinite number of repeated samples from the population and computing a mean for each sample. The mean's standard error turns out to equal the population standard deviation divided by the square root of the sample size, and is estimated by using the sample standard deviation divided by the square root of the sample size. For example, a poll's standard error (what is reported as the margin of error of the poll), is the expected standard deviation of the estimated mean if the same poll were to be conducted multiple times. Thus, the standard error estimates the standard deviation of an estimate, which itself measures how much the estimate depends on the particular sample that was taken from the population.
In science, it is common to report both the standard deviation of the data (as a summary statistic) and the standard error of the estimate (as a measure of potential error in the findings). By convention, only effects more than two standard errors away from a null expectation are considered "statistically significant", a safeguard against spurious conclusion that is really due to random sampling error.
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).
Homework Statement
Light is incident from glass (n=1.5) to water (n=1.33). Find out the range of angle of deviation for which there are two angles of incidence.
Homework Equations
Snell's Law
The Attempt at a Solution [/B]
The lowest value of angle of deviation would be 0° when i = 0. But, I...
I don't understand why does the standard deviation of a t-Distribution decreases as the degree of freedom (and, thus, also the sample size) increases when the sample standard deviation underestimates the population standard deviation?
I know that the standard deviation of sample = standrad deviation of population divided by sqrt(n) ...
However , in the following question , i don't know how to identify whether the standard deviation given is standard deviation of sample or standard deviation of population ... Can anyone help...
Homework Statement
If one bar of a histogram has been generated with ##n## entries from a total of ##x## measurements, i.e. the event occurs randomly ##n## times in the ##x## event interval, then what is the standard deviation of values in this bar? Let ##k## be the range of values that could...
Can someone guide me through the process of solving the following? Many thanks.
"Given the set {11, 12, 13, 14, 15}, by approximately how much does the standard deviation change if the least value is decreased by 2 and the greatest value is increased by 2?"
These questions are all over the...
Hi, All. I'm trying to re-familiarize myself with standard deviations. Any resources? I'm reading through the threads here and trying to figure out the following:
"n is a positive integer.
What is the standard deviation of 10 consecutive positive multiples of n.
And what is the standard...
Homework Statement
A supplier converts the weights on the cement packages she sends out from Ounces to kilograms (1kg = 35.27 oz).
How does this affect the standard deviation of the weights?
Homework EquationsThe Attempt at a Solution
[/B]
My ans is the standard deviation remain constant ...
Homework Statement
There are 15 numbers on a list, and the mean is 25. The smallest number on the list is changed from 12.9 to 1.29.
a. Is it possible to determine by how much the mean changes? If so, by how much does it change?
b. Is it possible to determine the value of the mean...
Regarding Einstein's static universe John Baez explains in The Meaning of Einstein's Equation
To see this, consider a small ball of test particles, initially at rest relative to each other, that is moving with respect to the matter in the universe. In the 13 local rest frame of such a ball, the...
I was given the averages (AVG) and the corresponding standard deviation (SD) of sets of data. I have no copy of the raw data for each data point that were used to calculate the AVG and SD.
I performed further data treatment on the data. I want to ask what is the relationship between the...
Homework Statement
Homework EquationsThe Attempt at a Solution
Let's denote the result of the throw by the variable x.
## <x> = Σ_i P_i x_i , i = 1,2,3,...,6.
\\= \frac{1+2+3+4+5+6}{6}
\\<x^2> = \frac{1^2+2^2+3^2+4^2+5^2+6^2}{6}
\\σ_x = \sqrt{<x^2> - <x>^2} ##
Is this correct?
I'm trying to write a computer program which generates a random list of numbers but the random numbers form a bell curve, that is, there is a mean and a standard deviation from that mean. I'm not interested in some function that gets the job done, rather I'm trying to understand how do you...
Homework Statement
For the five data 0, 7, 8, 10, and 10 find the standard deviation.
Homework Equations
https://forum.allaboutcircuits.com/threads/how-to-find-the-standard-deviation.138607/
I know the formula:
Z = (X-Mew)/Sigma
Sigma = Standard Deviation
Mew = Mean = 7
X= score?
Z= number...
http://www.nat.vu.nl/~tvisser/nonexponential.pdf
I always thought that an unstable system will decay exponentially but I recently learned that it obeys the quadratic law in the short time and power law in the long time. Can somebody tell me the equation that governs the quadratic law and power law?
I am working on a simulation of the solar system, but I am having problems with the orbits with Europa and Io shown in the image below, the orbits of Jupiter, Ganymede and Callisto are consistent with NASA's simulations. For all bodies I have used identical parameters in generating the initial...
Could someone guide me on the approach I need in resolving this question.
I have seen some online examples of the same question, but what is required in this is different. I'll very much appreciate your support.
Problem:
For boys, the average number of absences in the first grade is 15 with a...
Hey guys!.
I need to use this method of minimization.
The procedure to follow is explained here:
http://es.tinypic.com/r/35mmtg0/9
However, I do not fully understand. What do I have to do?
What I got from the paper is that I only have to minimize the equation 15.7.16, by using bisection. With...
Homework Statement
A company allows a maximum failure rate of 1 out of 250,000 parts. To insure this quality goal, failed parts must be how many standard deviations from the mean? Use Excel to solve.
Homework Equations
z= (X-μ)/σ
The Attempt at a Solution
Hi! So I'm assuming that this is a...
Suppose that I use a prism (vertex angle ##\alpha##) spectroscope to analyze a beam of visible light from a mercury lamp (different wavelenghts) and I want the determine the refraction index of the prism using the minmum deviation angles ##D_{min}##...
I have 2 signals:
signal1: https://www.dropbox.com/s/zr04pff9skeh8cn/TX.dat?dl=0
signal2: https://www.dropbox.com/s/h436a915dd99hln/RX1.dat?dl=0
signal2 represents for 20 measurements, each measurement combines with signal1 to get time delay estimation using xcorr.
So, I will have 20 delays...
Hey everyone!
I'm learning about some statistics and its past office hours with my teacher but I'm stuck on this problem.. I came up with 2.14% as the probabillity\final answer..
Could you guys give me your 10 cents on this?
Thanks again!
I have some problem understanding the section on "Geodesic deviation" in schutz, more specifically I'm confused by eq. 6.84:
Eq 6.84 reads (ξ is the 'connecting vector' from one geodesic to Another, V is the tangent vector):
We can use (6.48) to obtain
∇V∇Vξα = ∇V(∇Vξα) = (d/dλ)(∇Vξα) =...
I just wonder that why the negative deviation comes in graph except for hydrogen and helium gas.I am still thinking for the reason and searching for it.So please help me ...
Hi
Maybe my math/stat is very poor. I'm having trouble manipulating the standard deviation. Here's the thing.
I have radar mounted on a car. For each detection, the radar returns these variables.
- relative distance between the object/host vehicle in forward direction (in vehicle body-fixed...
I have a question regarding when to go for standard deviation σ or confidence interval ci. I am not sure of how to interpret ci. It seems to give me an option to choose the level of confidence, but I don't see why the the ci is divided by the root of the number of samples. Any pointers would be...
Hi all,
I learn some statistics some times ago. It has been while but I still remember some characteristics and property of the normal distribution. One of them is the standard deviation could be used to estimated the probability of finding the entity around the mean in the range ##[-n\sigma...
I am trying to calculate the unit vector and standard deviation of the signal. I hope everyone can give me ideas.
Here is my scenario:
I have 2 rx channels: - f is channel 1 with the length 1x256 complex, then FFT. - g is channel 2 with the length 1x256 complex, then FFT. - from f and g, I can...
I just looked up the standard deviation formula. I makes quite sense to me because we're actually trying to 'measure' how much all the observations deviate from the mean value. To do this, we calculate all the possible differences, [X(mean) - x(i)], then we square all the differences to get rid...
Homework Statement
Joan’s finishing time for the Bolder Boulder 10K race was 1.75 standard deviations faster than the women’s average for her age group. There were 405 women who ran in her age group. Assuming a normal distribution, how many women ran faster than Joan.
Homework Equations
The...
Homework Statement
This is not homework. This is a question given in class with the answers already given. Neither the teacher nor the students have been able to figure out how to obtain the answers though, so my question is how to find them?
Here is a picture of the question.
The standard...
The King of the Hill triathlon race in Kinsale consists of
a 750 metre swim, followed by a 20 kilometre cycle, followed
by a 5 kilometre run.
The questions below are based on the data from the 224
athletes who completed this triathlon in 2010.
Máire is analysing data from the race, using...
*WARNING* My understanding of maths is pretty limited and i don't know if i am being really stupid or not.
Ive been looking into data analysis of football matches, working out proabilities of certain situations happening and how steady the averages are. i come across a website which as really...
I'm a beginner with the study in data analysis in Physics. I'm trying to understand the meaning, in the field of experimental Physics, of the standard deviation ##\sigma## of a series of data.
There is one fundamental thing about ##\sigma## that I read but I could not understand.
>In a series...
Centrifugal force due to rotation of the Earth has among its effects the deviation towards the equator of a ball falling from height ##h## vertically on Earth.
I do not understand what is the inertial explanation of this phenomenon. Once the ball is released there is no centripetal force that...
I understand(or assume understand) that geodesic deviation describes how much parallel geodesics diverge/converge on manifolds while moving along these geodesic. But is not it a definition for intrinsic curvature? If it is same as Riemann curvature tensor in terms of describing curvature, why...
Hi,
I have a question from my germanium lab, which is how to estimate the max deviation (non linearity ) of a system.
I plot the relation between the deviation of the energy as a function of true energy and got this ( see pic), but didn't know what to do next.
Thanks.
Hi,
I'm working on some coursework for which I have been modelling a curve to a set of points, and for the final section I am wanting to calculate how close each point is to the curve as a method of comparison between the curves I have calculated. Some of the curves are quadratic, and others are...
Suppose i have a random variable X and its standard deviation dx. We could write the average with error like $$<X>\pm dx/2$$.
But how do we know it is centered or not ? It could be +1/4 -3/4 for example.
When I was solving questions on Ray optics I encountered a question wherein I had to prove that when a ray of light undergoes minimum deviation through a triangular prism then both the angles of refraction that is the first one at the incident point and the second one at the emergent point...
I was studying in my math textbook about these two methods to measure dispersion and variability in data. I was able to understand mean deviation that it's the average by how much a quantity deviates from mean but I was unable to understand standard deviation. Also, as standard deviation squares...
Hi everyone, I have a basic question on statistics.
Suppose you have a biological assay to test a given property of some molecules.
At some point in time you have tested N different molecules M1, M2, ..., Mi, ..., MN, and for each you have repeated the test a number of times Ri. The results are...
Homework Statement
Find the formula for the standard deviation (s_h) of heading angle, given the north and east standard deviation of position of two points (s_n1, s_e2, s_n2, s_e2), each point's north-east covariance (s_cov_ne_1, s_cov_ne_2) and the north and east distance between them (d_n...
Any help would be much appreciated:
My data is grouped into 42 categories according to classification of bird catch. Each group contains "X" amount of species, but for ease of input we categorize them into subsets. For example:
Group 1: 265.5 kg
Group 2: 47 kg
Group 3: 213.5 kg
etc...
The best known effect of birefringence is the lateral displacement of the extraordinary image. Why is this effect rarely quantified? I couldn't find a table of materials specifying the deviation angle δ of the extraordinary ray (say, for an angle of incidence equal to zero). Birefringence seems...
At the moment I'm in the final stages of my doctorate in mathematics. (My background is a BS in physics and an MS in mathematics.) My focus and interest have been in applied functional analysis in general and various kinds of abstract and concrete delay equations in particular. These are...
I had a question about how to properly perform error analysis on a series of distance measurements. I need to find the relative error in the distance. I was wondering, should I use the instrument uncertainty divided by the measurement (in this case, it would be 0.005m / (mean measurement)). Or...
Hello to all of you.
I have the following case to solve.
I have three overhead power line towers. The first and the third are with tension insulator strings, and the second is with suspension insulator string.
During the design process i noticed that the second tower is located incorrectly and...
Hello,
Upon following advice from BvU I'm starting a new thread to request help on a concrete issue I have. I have a container with 12x8 wells. Each well contains a roughly equal amount of bacteria. The bacteria are fluorescent, and I am trying to quantify their fluorescence as precisely as...