Questions tagged [data-analysis]

Use for question relating the the techniques of data analysis.

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JLA SNDATA working [closed]

Does anyone know how to use Joint Light Curve Analysis (JLA) SNData module (including the download)? I tried to look at the documentation http://supernovae.in2p3.fr/sdss_snls_jla/ReadMe.html#sec-2 ...
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Error calculation for a relative difference with only one standard deviation (STD)

I have a quantity that is calculated with two measurements, but I only have a tabulated standard deviation for one of the measurements. How would I calculate the error on the calculated quantity? The ...
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Ambiguous propagation of uncertainty

Suppose I have a voltage versus current graph with various "peaks" in current at given voltages. For example, this is what is seen in a Franck Hertz experiment. I can measure the value of ...
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Where does the error from Origins fitting come from?

Im using Originpro to do some linear fitting of my data points. Origin calculates the gradient and gives an error. Where does this error come from? Ive assumed its how much the data points are ...
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Different fitmodels for different intervals

A number of points were measured and plotted on an XY graph. I want to have the best fit line for this graph. The best fit model for the first part of the graph is described by some function $f_{1}\...
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How to quantify the uncertainty of the time series average?

Usually, we measure a fixed physical quantity, then we simply average MEAN on the measurement results and calculate the standard deviation STD, then the measurement result can be written as MEAN±STD. ...
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Total standard deviation for a set of measurements

I have a doubt about the calculation of the standard deviation for a set of measurement. To explain better what I mean, I will illustrate what I am doing in my experiment. I am collecting the spectra ...
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What is the difference of two Chi-square formula, and how can I use them properly?

I found two formula for chi-square: $$\chi^2 = \sum_i ^N \frac{(\text{measured}_i - \text{expected}_i)^2}{\text{variance}}$$ and $$\chi^2 = \sum_i ^N \frac{(\text{measured}_i - \text{expected}_i)^2}{\...
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How the Zero-point Energy of the System containing 2 Fermions in 3 Micro-Energy States is 1?

If we distribute 2 Fermions $\mathrm{(A,A)}$ in 3 Micro-Energy States (0,$\epsilon$,$2\epsilon$), the confirmation is given by : $$ \begin{array}{|c|c|c|c|c|} \hline 0 & \varepsilon & 2 \...
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How to compute errors from a fit?

I have a set of data with errors, how do I compute the error for the fit $f(x)=a$? I remember there are formulas for the errors in parameters for fit $f(x)=ax+b$, i.e. $\delta a$ and $\delta b$. Where ...
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Data analysis of ratios

I am analyzing some observational data which includes the ratio of masses (two masses for the same object, but measured using different methods). In principle, it is largely arbitrary whether one ...
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How to correct for periodic errors in data set (worm motor)

I have a monochromator produced by Bentham which I am using for my physics experiment. This runs through the wavelengths in steps of what I thought were exactly 1nm. To calibrate the monochromator I ...
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In a least squares fit, is the resulting error in the fit parameters considered statistical/random error or systematic error?

In a least squares fit, if there is no error estimate on the input data points, is the resulting error in the fit parameters $\sigma_y$ (which is calculated from residuals) considered statistical/...
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Calculating Coherence Length and spectral width given an interferogram

I'm currently doing a lab in which we use a Michelson-Morley interferometer to analyse different light source. One of the mirrors in the interferometer is moved by a stepper motor. One of the light ...
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Comparing the variance of the position of particles of a sample of matter with the sample's temperature

As the title suggests i have attempted comparing the variance of the position of particles of a sample of matter with the sample's temperature. Now firstly we need to clarify the basics: method for ...
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Least squares fit versus averaging

Suppose I want to find the spring constant of a spring from measured $F$ and $x$ data points. There are two basic ways to do this. I could calculate the spring constant for each data point and ...
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What does the inverse background efficiency represent?

I am reading a paper from the ATLAS experiment on the identification of tau jets from background jets and came across this figure: I am struggling to find what the formula is for the inverse ...
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Determining the appropriate number of significant figures to report in least squares analyses

I'm tasked with fitting a set of data to a line using Excel's $\text{LINEST}$ least-squares fitting routine. The data are $l$ and $m$ values, assumed to follow the relationship: $$l = l_0 + {g\over k}...
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Data science for physics recommendations

As a mathematical statistics student, I was wondering about learning data science application for physics, in general probabilistic modelling for physics. I don't mean that much engineering ...
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Displacement distribution Molecular Dynamics

I have a file "traj.dat" with the trajectory of $N$ particles for $M$ frames separated by $\Delta M$ steps (with a time-step $\Delta t$). I often compute Mean Square Displacement (MSD) of ...
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Utility of Topological Data Analysis in Theoretical Physics

I audited a lecture on Topological Data Analysis, and I found it really interesting, primarily because of the connection to algebraic topology. I asked the professor if there are any connections to (...
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3 answers
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Validity of power law fit (and analytical fit choice)

Context I am carrying out molecular dynamics simulations of trapped ions in a radio-frequency field of amplitude $U_{RF}$ + DC (see details https://arxiv.org/abs/2102.04098). I am studying radio-...
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Fitting time resolved data with a convolution

I want to fit experimental data of a time dependent Signal. The Signal is the result of a concentration convolved with a pulse. But the question is more in general, so I hope the picture below will ...
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Cross correlation for the fluctuating part of two timeseries. Can it attain values gretaer than unity

I have written a code to estimate the lagged cross correlation between the fluctuating parts of two quantities $(X, Y)$. To estimate the fluctuating parts I am using the following equations: $X^{'}(t) ...
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Uncertainty propagation time difference

So for an experiment we gathered time data. It a rolling object, where t2 and t1 are measurements of one whole roll of circumference. We estimated time uncertainty at 5 ms. ​ So then estimation of ...
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Fitting of experimental data affected by different kinds of errors

It is quite easy to evaluate the best-fit curve for a set of n data points when the dependent variable is affected by a statistical error (namely when you have n triplets $(x_i,y_i,\sigma_{y_i})$. I ...
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Galaxy filaments data access

I'm a PhD student in applied mathematics seeking to analyze geometric structure of galaxy filaments and walls, specifically the curvature and branching nature of the filaments and walls. I'm curious ...
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How do I know which linear fit is better?

Let's say we have a simple mass/string harmonic oscillator. Measuring the period of the movement, I can calculate the angular frequency. Knowing that $$\omega = \sqrt{\frac{k}{m}} \qquad \text{and} \...
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How to turn a time axis into a frequency axis?

I'm currently trying to obtain the temperature of a rubidium cell that I used in an experiment. I performed a Gaussian fit on my data but now I'm supposed to take the differences between the peaks to ...
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How do you weight a chi square for uncertainties in $x$ and $y$ (different units)?

So I have experimental data for energy vs angle with uncertainties in both the $x$ and $y$ direction for every point. I am comparing this to a known curve/data points. Is it possible to calculate a ...
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How do you determine these coefficients experimentally?

So in our lab today my friend and I had to examine the time it takes for cylinders to roll down an incline. We managed to find an ansatz on the following form after some work: $$ t = c(c_1 + x^{c_2})^{...
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What does "a least-squares approximation to a sequence of data is simply their averaged value (mathematical expectation)" mean?

I am reading the paper "Multiscale coarse graining of liquid-state systems" (https://doi.org/10.1063/1.2038787). In the paper, right after equation (1), they say "a least-squares ...
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Best Fit with linear function and a problem of "zero"

I have experimental data on the dependence of the magnetic field (B) in the center of the Helmholtz coils on the current in it(I). ...
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Public data to practice data analysis skills

Apologies if this is the wrong place to ask this, but I am currently trying to brush up on my data analysis skill in python as I am applying to data science jobs. I am trying to find some data that I ...
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How to calculate energy loss from falling balls?

Good evening, I am doing a science investigation about "Which surface will affect the energy loss of a bouncing basketball the most?" and I am having trouble calculating the energy loss for ...
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A question on the RMS of a "Gaussian" Distribution

We suppose to have this "gaussian" distribution: with $mean=1217.60 [ch]$; and $RMS=143.65 [ch]$; where [ch] is channel. The question is, the error over the mean is: $\pm \sqrt{RMS}$? And ...
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Reduction of the standard error in a magnetometry experiment

I have to answer this question for my physics lab, but our lab is about the mean, standard deviation, and standard error on the mean, and I see absolutely no connection to this. Here is the problem: &...
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35 votes
7 answers
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How seriously can we take the success of the Standard Model when it has so many input parameters?

The Standard Model of particle physics is immensely successful. However, it has many experimentally fitted input parameters (e.g. the fermion masses, mixing angles, etc). How seriously can we take the ...
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Is the following methodology to find the error metrics between the two curves technically sound?

I am comparing two curves, one of which is derived from physical experiment, while the latter is obtained from a simulation. The experimental curve was used to calibrate the simulation results. The ...
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What is the 'correct' way of determining uncertainty of an average value from multiple measurements?

I am very confused as to what the correct way is to calculate the uncertainty of the average of values ($x_{avg}$) in a data set of measurements $(x_1 ... x_N)$. I have found at least four different ...
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Floating Normalization of Experimental Data Sets while Fitting Multiple Models

I have $N$ data sets of unequal cardinality, and I am told we do not treat each data set with a normalization of $1$. Instead we let the the normalization float and fit it as though it were any other ...
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Usage of $t$-test in HEP experiments

I was brushing up on some statistics and thinking about what I'd learned in my undergraduate degree, which is what led me to this topic: Is the (Student's) $t$-test, and $t$-distribution used anywhere ...
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On regressing data, should the $y$-intercept be forced to a value according to the model?

I have a theoretical model of the form $$y=kx$$ Say I experimentally measure the data pairs $(y,x)$, from which I want to determine the value of $k$. I am using the curve fitting feature of MS Excel (...
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1 vote
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Struggling to find an approximation for these experimental values

I'm looking for the formula that best approximates these experimental x-y values: A correct answer should present asymptotic behavior on both the X and Y axes. Y should approach infinity as X ...
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12 votes
2 answers
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Why don't we use absolute error while calculating the product of two uncertain quantities?

I've found a rule that says, "When two quantities are multiplied, the error in the result is the sum of the relative error in the multipliers." Here, why can't we use absolute error? And why ...
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1 answer
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Statistics for analysis in Physics

While I am well aware of the branch of physics called statistical physics my question does not pertain to this. My background is bioinformatics which very rarely uses causal modelling instead we tend ...
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How is number of photons found on a spectra?

Sorry for the stupid question, but I am very new to this and have no background in physics. Say we have a spectra as the one in the image, which represent a charge distribution over a specific channel,...
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Needed precision for detecting effects in experiments

I did a bayesian fit to experimental data with a physical model. I notice that some effects cannot be detected due to the precision of the data and the physical model doesn't fit in the best way. So I ...
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Difficulty bounds in a white noise model

Suppose we make a measurement in a real/virtual experiment for which the noise is given by a white noise (Gaussian) model. Suppose also that we have a very good filter or machine learning (ML) model ...
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How can I process many time series to determine which are oscillating?

I have a simulated system of many particles (440) and want to determine if any of their velocities are oscillating or showing oscillatory behavior. I've tried looking at each of the velocity time ...
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