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1
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1answer
76 views

Fitted Beta distribution always holds water. Can I force it not to?

I am trying to fit a beta distribution to election forecast data. The ultimate purpose is determining with what probability the election will be decided by one vote (more on this here). My data is as ...
1
vote
1answer
53 views

Predicting continuous output

I'm trying to predict output per worker for given inputs of capital (physical capital), labor (human capital) & productivity. I have a data set of several countries ...
0
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0answers
9 views

fitting a non-linear curve with one parameter

I have an equation: $\ddot{x}+(\delta+\epsilon\cos{t})x=0$ known as the Mathieu equation.The $\delta-\epsilon$ parameter space of this equation looks something like The red lines in this diagram ...
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0answers
23 views

How can I assess if a parametric model can reproduce the same curve with different parameters?

I have a parametric model that I think it is "degenerate" in the sense that I can obtain the same model with different parameters. For example, if I have a convolution of two 1D Gaussians (say, G1 ...
1
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0answers
9 views

Testing hypothesis about the location of the maximum point on a curve

I have data from an experiment on the relationship between PPI (the dependent variable, a measure of startle reflex attentuation by weak stimuli) and SOA (the main independent variable; it's the time ...
2
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0answers
56 views

Fitting a logistic curve to cumulative data using glm()

I'm trying to fit a logistic curve to cumulative data, derived from satellite imagery. Previously, I have point observation data which were either 0s or 1s. Os being 'forest' and 1s being ...
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0answers
30 views

Approximate Probability Distribution Function

I am trying to approximate a large discreet probability distribution function using a histogram with a small number of entries. I.e., create a piece-wise first-order polynomial approximation for a ...
1
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0answers
34 views

How should I report the significance of a spline smooth obtained using mgcv in R?

I wish to test whether a spline-based smooth could be replaced by a linear term. I am using the mgcv package in R. Using the example from the helpfile: ...
1
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1answer
54 views

What distribution family would best fit this graph?

Sorry if this type of question is not kosher. I'm new around here, so please forgive me. Anyway, I have a dataset that describes the probability that users will like certain articles from my corpus ...
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0answers
21 views

How should I fit this data?

I have a dataset: ...
6
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0answers
129 views

Applying a variance-stabilizing transform to a fitted function (rather than data)

Outline I'm working with data corrupted by a mixed Poisson-Gaussian noise model (for example with images gathered in astronomy or electron microscopy), and have been using the generalized Anscombe ...
0
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0answers
7 views

Looking for catalog of “mechanism classes” that give rise to specific curve shapes

(I apologize for the length of this post. I don't know how to frame the question more succinctly.) I have some experimental data, in the form of a collection of curves with fairly little noise, ...
1
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0answers
55 views

grofit package for growth curves and prediction?

I am trying to use grofit package for biological growth curves. I would like to see which curves describe best my data and from them predict results I don’t have. I basically have a sample of data ...
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0answers
19 views

Types of growth curves that can be compared using statmod compareGrowthCurves

I'm using the function compareGrowthCurves in the R package statmod, but I can't seem to find an explanation of what types of curve this is valid for. Does anyone ...
4
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1answer
297 views

Total least squares curve fit problem

I am trying to fit a quadratic curve across a scatter plot of two variables. Since both variables are noisy I cannot use an ordinary least square regression (OLS) and I would like to have a ...
3
votes
1answer
49 views

Distribution based on rate of distinct values

I am investigating the following problem: I have a large set of values, many of which are repeated. Measuring the number of distinct (or unique) values shows that their number grows much slower than ...
2
votes
1answer
37 views

Confidence interval for a constrained fit to Gaussian-like data

I'm working with data from an instrument which is expected a priori to produce Gaussian (normally) distributed data: \begin{equation} G = A\exp\left(-\dfrac{(x - \mu)^2}{\sigma} \right) ...
7
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1answer
142 views

Given loads of data, can we always model it with polynomials?

Given Taylor series and enough data so as to not risk over-fitting, do you actually need to think about if your phenomenon is following an exponential, quadratic, logarithmic, ..., behaviour? I'm sure ...
2
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0answers
38 views

How to approximate error on Chi-Squared Fit when bin counts are zero

I am using a galaxy image simulator that provides a 2D histogram that has the number of photons per pixel (bin) $N$. I am currently using a least-squares residual: $\sum_{bin}(f_{data}-f_{model})^2$ ...
1
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1answer
29 views

Approaches for extracting single-year age estimates from age-buckets

I'm trying to estimate a binary function of $Y$~$Bernouli(p_{i})$ where $p_{i}=f(age)$ where f is an unknown continuous function. There are obviously a lot of methods to try to reconstruct f (splines, ...
3
votes
1answer
113 views

N-sigma curves for a non-linear least square curve fit

I'm using python's scipy.optimize.curve_fit routine (which uses a non-linear least squares) to fit an exponential function of the form: ...
0
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0answers
48 views

How to corretly scale sum of squared residuals of two different sets of data in order to compare them?

I did numerical simulations of two different systems that returned me N=1000 histograms expressed as $\{x,y,y'\}$, where $x$ is the independent variable, $y=P(x)$ is the probability distribution ...
0
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0answers
9 views

Weighing data during distribution fits

I currently have multiple sets of data in the form of a histogram. Using Matlab, the all look to be very well described by the negative binomial distribution. However, the far right tail not modeled ...
2
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1answer
52 views

Finding analytic form for distributions using linear regression, need ideas

I'm trying to find an analytical form to describe these probability density functions: I'm pretty new to all of this, but think I should use some linear combination of basis functions (so I can then ...
0
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0answers
137 views

Fitting for a Poisson-Gaussian Mixture Distribution

First of all, I am rather new to statistics, so go easy on me. I am aware that the negative binomial distribution can be thought to arise as a result of letting the $\lambda$ parameter in a Poisson ...
2
votes
1answer
112 views

How to fit a mixture of Gamma distributions to the PMF of a discrete distribution?

I have a PMF of some discrete distribution that has been numerically computed. Note that I do not have any samples to work with here, so techniques like Maximum-Likelihood and Expectation-Maximization ...
2
votes
1answer
102 views

How to draw a tangent line to a curve fit?

I fitted my stress-strain data with cubic fits as shown in the figure below and added the corresponding straight lines (dashed and same color). The problem is I put these straight lines at my own ...
1
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1answer
63 views

Forecasting temperature using CurveFitting

I am assigned with a academic task to forecast temperature using CurveFitting. Please suggest me whether I use Linear regression/ Non-Linear regression or extrapolation? I have to forecast 1 next ...
6
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1answer
133 views

Gaussian mixture regression in higher dimensions

Problem: I have a discrete representation of a surface/height-map $z = f(x,y)$ that i want to model as a mixture of gaussians (please take probability distributions out of your mind for a moment). ...
0
votes
1answer
30 views

Number of points crossed by their best fit line

My lab teacher asked this question in class, but i find no way to work it out. If I have $n$ points with their uncertainties, I know that they follow a linear expression and I find the best-fit line ...
1
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0answers
63 views

Alternatives to constrained non-linear optimization: a case study with Gaussian curve fitting

I have a set of data points distributed like a bell-shape curve with varying amplitudes and widths. I need to parameterize these data points and a Gaussian with amplitude, width and offset parameters ...
0
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0answers
49 views

How to compare forecasting methods: based on ARIMA and curve fitting?

I'm making a project connected with identifying the dynamics of sales. My database concerns 26 weeks (so equally in 26 time-series observations) after launching the product. I want to make forecast ...
2
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0answers
43 views

Which steps have to be done before fitting logistic curve to time-series?

I want to cluster time-series concerning sales of products. In the database I have 26weeks after launching each products and units sold each week. One of the method of clustering is to cluster ...
0
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0answers
23 views

Skewed, humpy, left tail doesn't approach 0

Self-learning statistics by fiddling around with some modeling. Having trouble finding distributions for this data however. Defined for $x >0$ $P(0) > 0$ $P(X) \to 0$ as $X \to \infty$, (very ...
0
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3answers
349 views

Multi-peak Gaussian fit in R

I have a large data set composed of several "independent" data frames like this one ...
0
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0answers
31 views

Negative values in the data set

I have a set of negative values and would like to put a fitted model in R. How would I approach it? Say, I want to use Gamma distribution as a fitted curve using method of moments but the data is all ...
0
votes
1answer
110 views

Fitting logistic function with pymc

I've asked this question on stackoverflow too, but no answer yet. This seems a more appropariate place to ask this question: I'm messing around with pymc to understand it a bit better. Now I am ...
4
votes
1answer
87 views

How can I estimate the shape of a curve where the predictor variable is right censored interval variable?

Are there methods available to conduct interval-regression style analysis where a predictor variable is the interval variable and the outcome variable is a dichotomous variable? To give a bit of ...
0
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0answers
53 views

Minimum points required for fitting curve

If I need to build yield curve, n what is the minimum number of data points necessary for any interpolation method, e.g. say cubic spline or Nelson–Siegel, etc. I ma not sure if I can raise this ...
0
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0answers
22 views

Least-squares, pivoting/rotating around a reference point?

Suppose I have two datasets $y1$ and $y2$ sampled equally on $x$. I would like to bring $y2$ in register with $y1$ in a least-squares sense, and referenced to one point at $x_{ref}$ in $y1$ (i.e. the ...
1
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0answers
53 views

Deep and sparse vs. Thin and dense data collection for curve fitting?

I'm designing a toy experiment in which I'd like to model the 'attractiveness' of a credit card as a function of the interest rate it comes with: Attractiveness will be reported on a 10 point scale ...
1
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0answers
46 views

Minimizing the sum of squares of autocorrelation function of residuals instead of sum of squares of residuals

I am trying to fit my multi-exponential model to some experimental data and I am using a simulated annealing algorithm. My objective function has so far been the sum of squares of the residuals: ...
1
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0answers
47 views

Fitting a parameterized 2D distribution

I frequently deal with datasets that rely on a binary classification based on a Pulse-Shape-Distribution (PSD) discrimination value. This is based on a 2d fit of the PSD value vs the amplitude of the ...
0
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0answers
49 views

Fitting a Non-Central t-Distribution with Location and Scale Transformations

I am trying to fit a distribution function to empirical observations that have the following properties: Non-zero mean Non-unit variance Heavy tails Asymmetric about the mode I am considering ...
1
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0answers
138 views

Linear-logarithmic Regression in MATLAB with two input arguments - which model to assume?

Look at the following plot and ignore the solid lines please (just look at the dotted/dashed ones). ONE curve is described by the following parameters and ONE fixed value for the second input ...
5
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1answer
111 views

Fitting distribution to spatial data

Cross posting my question from mathoverflow to find some stats specific help. I am studying a physical process generating data which projects nicely into two dimensions with non-negative values. ...
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0answers
33 views

Fitting Inspection Time Data to Curve

I have a set of Inspection Time data that consists of two variables: SOA (stimulus onset asynchrony) and Accuracy. This data refers to how accurately you can perform on a simple stimuli ...
3
votes
1answer
234 views

Find out if there is a way to create BMI weight category variable

I am working on a project and have to find a way to break my data into percentiles. The variables that I already have are gender, age in months and BMI. If I am able to calculate the percentile that ...
1
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0answers
57 views

Fitting a model to correlated data

Trying to fit a model (bloch equations from MRI) to experimental data (12 parameters, 12 equation). Monte Carlo Multistart ('lsqcurvefit' in MATLAB) gives expected values for all parameters except for ...
0
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0answers
29 views

Fitting a function to data with correlated errors

I have a question regarding fitting a curve to data with correlated uncertainties. Suppose I have 8 bins each with uncertainties (img below). The green line is theory curve I am trying to fit with a ...