What is Error bars: Definition and 28 Discussions

Error bars are graphical representations of the variability of data and used on graphs to indicate the error or uncertainty in a reported measurement. They give a general idea of how precise a measurement is, or conversely, how far from the reported value the true (error free) value might be. Error bars often represent one standard deviation of uncertainty, one standard error, or a particular confidence interval (e.g., a 95% interval). These quantities are not the same and so the measure selected should be stated explicitly in the graph or supporting text.
Error bars can be used to compare visually two quantities if various other conditions hold. This can determine whether differences are statistically significant. Error bars can also suggest goodness of fit of a given function, i.e., how well the function describes the data. Scientific papers in the experimental sciences are expected to include error bars on all graphs, though the practice differs somewhat between sciences, and each journal will have its own house style. It has also been shown that error bars can be used as a direct manipulation interface for controlling probabilistic algorithms for approximate computation. Error bars can also be expressed in a plus-minus sign (±), plus the upper limit of the error and minus the lower limit of the error.A notorious misconception in elementary statistics is that error bars show whether a statistically significant difference exists, by checking simply for whether the error bars overlap; this is not the case.

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  1. F

    I Error bars in Excel (standard deviation, standard error, percentage)

    Hello, I was working in excel on data reported in two columns, X data and Y data. I measured both X and Y, i.e. Y was not calculated using a function and the X data. The Y an X data was plotted as Y vs X using a scatterplot. The Excel graph offers the option to add error bars over each point...
  2. T

    Is it okay to add error bars into a histogram plot?

    I made a histogram based off a dataset and I calculated the uncertainty of the measurements and I included the error bars into my histogram. Is that okay? I am asking because I never seen error bars included with a histogram. I have included an image of my histogram below:
  3. Amy_93

    I Statistic uncertainties in cross section plots - how to calculate?

    Hi there, I hope I chose the right forum for my question. So, basically, I'm doing an analysis measuring the number of signal particles in a certain momentum bin i, and doing two corrections: Nsig, i=M*(Nmeas, i-Nbkg, i) Here, M is a matrix covering PID correction and PID efficiencies, and...
  4. A

    I Uncertainty of MonteCarlo Simulations: Weight and Error Bars

    Hello everybody, I need a help, primarly a confirmation about my reasoning. I have data from a MonteCarlo simulation of collisions between particles at LHC (made with Madgraph). I have plotted some variables, for example the angle between two final leptons. Then I have normalized the plot to a...
  5. SuchBants

    Uncertainty in the intersection of two lines with error bars

    The only thing I wish to take from this graph is the intersect of the two lines of best fit. How can I get the uncertainty in this point? While the points appear to have the same uncertainties, they actually each have their own distinct % uncertainty. Would the maximum uncertainty in the X...
  6. Hi Im Paul

    Graphing Data in Excel: Error Bar Confusion

    I'm currently writing a paper over an experiment I did for class and I have a very stupid question over I need clarification on before I continue. I am using excel to graph out data, and I have determined that the error in my Length is .001 m. However, I am graphing the inverse of length to...
  7. S

    I The error bars of redshift drift

    Dear all, I am reading the paper "Cosmic dynamics in the era of Extremely Large Telescopes " by Liske et al. about redshift. I get the physical meaning of redshift drift, but when it comes to the error bars, I am confused. - Aren't the error bars given in equation (15) ? - Isn't this function...
  8. Jamison Lahman

    I Pie Charts & Error Bars: Which to Use?

    Kind of a silly question; can pie charts have error bars? I have used x-ray dispersion to find the approximate chemical composition of unknown samples. Is it appropriate to have error bars on how much we expect the percentages to deviate statistically throughout the sample? Or, should I go a...
  9. E

    B History of Error Bars in Physics

    I was reading an 1803 paper by Thomas Young (of double slit fame), "Experiments and Calculations relative to physical Optics". In it, he lists various dimensions of fringes of light and things. All without any error bars. It got me thinking, what's the history of error bars in scientific...
  10. J

    I in deciding what my error bars should be

    So, we did an experiment to find the dissolved oxygen concentration in % over time in a stirred tank reactor at 2 different flow rates and at 3 different agitator speeds. We did not do any repeat measurements, it was just one reading per condition. Now I am confused what sort of error bars I...
  11. Orodruin

    Insights Plus/minus What? How to Interpret Error Bars - Comments

    Orodruin submitted a new PF Insights post Plus/minus What? How to Interpret Error Bars Continue reading the Original PF Insights Post.
  12. D

    Error bars, Chi square distribution

    Hi, I'm doing a fit using Chi-square distribution. I have a data set and their errors, I found the best estimate minimizing Chi square, as usual, and I like to found the error bars of my best estimates but I don't know how to do that. Which is the standard form to do it?
  13. J

    Finding uncertainty for varying error bars

    Homework Statement I am currently doing an experiment on Compton scattering and have plotted a linear graph of 1/E' on (1-cos θ), where E' is the scattered gamma ray energy. My goal is to find the value of the gradient and y-intercept with their corresponding uncertainties. Instead of using the...
  14. D

    Fitting a curve to data with error bars on curve parameters

    I have several data points with error bars, and these error bars are different sizes for each of the data points. I'd like to fit a model function to them which has non-linear parameters, and be able to get error bars on the model parameters, ie. if my model is something like f(x) = A +...
  15. A

    Add Error Bars to Individual Points in Excel 2008 for iOS

    Hi, Okay, I'm in a bit of a rush: Can you put error bars on INDIVIDUAL points in Excel? I found the "custom" setting for the error bars, but you can only add custom error bars for ALL points. I'm looking for a way to mark errors for each point individually. Is there any way to do that? I...
  16. C

    Excel Problems with error bars

    I have a graph which I would like to add Y error bars to. When I click to add the error bars, it only allows me to add horizontal bars. This is very strange because the other graph I have, it allowed me to insert vertical bars. Basically when I click on exactly the same menu to insert error...
  17. M

    Curve-fitting to data with horizontal/vertical error bars

    Hello I've measured some data, let's say f±Δf as a function of x±Δx, and I know the form of f(x) but not the specific parameters, so it will be something like f(x) = (A/x)*exp(-B/x + C), I think. I'm comfortable enough fitting the data (x,f) to the curve and finding A,B,C, but can anyone point...
  18. H

    Does the use of error bars pertain to this experiment?

    I'm currently performing a real bench experiment that would essentially validate the results of those generated in two different computer models. Essentially, there is one (real) test setup, one computer model, and another (but different) computer model. I have ONE result from each of the...
  19. F

    Converting Errors for Logarithmic Graphs for Scientists

    I think this is probably the right place to put it, didn't really fit anywhere else. I've got the joyless task of writing a lab report at university and need to put a graph in it, ideally with error bars. I don't have a problem with error bars normally, but I'm coming unstuck about what to do...
  20. R

    Understanding Error Bars on Least Squares Fit Line

    Hello, What are the error bars on the least squares fit line? recall the variables are: x ; y ; x^2 ; xy ; y^2 ; yi=mx+c ; d =(y-yi) ; d^2 --------- is it d? Thanks
  21. L

    Variance (error bars) with a binomial proportion

    I have a list of chemicals, their assay test results, and a binomial column of whether or not the assay test result was high enough to be considered a threat (anything >2g/ml). Some chemicals were tested more than once, but others were not. It is understood that it is a poor set of data, but I...
  22. Simfish

    MATLAB Linear Least Squares Fit with Error Bars: A MATLAB Tutorial

    With MATLAB or something. Basically, I just have a bunch of data points where I should do a linear least squares fit, but each of the points have error bars around them.
  23. T

    Linear regression with asymmetric error bars

    I've been trying to figure out how to do a linear regression on data with asymmetric x and y error bars (different for each data point). Any help would be much appreciated.
  24. deccard

    Measurement error analyses, fitting min/max slopes to data with error bars.

    I have measurement dataset (x_i,y_i) -pairs with error for each value \Delta x_i and \Delta y_i so that I can plot datapoints with vertical as well as horizontal errorbar. I want to fit linear regression line y=a_1 x + a_0 and also error lines to the data. But how I take into account as...
  25. C

    Help with drawing gradients along error bars

    Homework Statement I have a set of data which clearly shows a linear trend. I've hand-drawn the y-axis error bars for the data (x-axis errors are negligible), and a trendline (without any mathematical/statistical techniques). The trendline stays well within each of the error bars...
  26. C

    How to Construct Best Fit, Min and Max Slope Lines with Error Bars for Graph?

    Error bars and slope error ?? Homework Statement I have to construct a graph with three lines. The middle line is 'best fit', one line is 'max slope' the other 'min slope', and error bars need to be drawn. The error for the Y axis is too small to draw so there is only an error bar for X...
  27. Monique

    Including error bars in a chart

    Can anyone recommend some free software to me where you can make charts that include an error bar? OpenOffice Calc is not able to do that (I don't have access to Excel). So as an example: I have a triplicate measurement of 77, 75 and 76. I want the graph to show 75 as the mean and then an...
  28. Nim

    Need WMAP error bars for CMBFAST power spectrum output

    From Kosmoi.com/Science/Cosmology/http://kosmoi.com/Science/Cosmology/Big_Bang/wiki.shtml "A critical further prediction was that the further away one looks, the hotter the universe should appear to be (as looking further away corresponds to looking backwards in time), and at some extremely...