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7 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
42 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
28 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 ...
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0answers
24 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: ...
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1answer
53 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: ...
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0answers
126 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 ...
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0answers
6 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, ...
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0answers
44 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
16 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
217 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
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1answer
41 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
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1answer
33 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
130 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
31 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: $\sum_{bin}(f_{data}-f_{model})^2$ ...
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1answer
28 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, ...
2
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1answer
78 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
39 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 ...
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0answers
8 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
48 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 ...
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0answers
114 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
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1answer
103 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
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1answer
85 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 ...
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1answer
61 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
125 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). ...
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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 ...
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0answers
56 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 ...
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0answers
44 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 ...
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0answers
41 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 ...
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0answers
22 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 ...
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3answers
277 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
29 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
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1answer
102 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
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1answer
82 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 ...
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0answers
47 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 ...
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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 ...
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0answers
51 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 ...
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0answers
43 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: ...
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0answers
42 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 ...
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0answers
48 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 ...
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0answers
120 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 ...
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1answer
104 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
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1answer
213 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 ...
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0answers
55 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 ...
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0answers
27 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 ...
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0answers
159 views

How do I regularize Python scipy's curve_fit when performing linear regression?

I have recently become proficient at using Python/scipy curve_fit to perform linear regression. However, with higher order ...
0
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0answers
46 views

Generating artificial experimental data to test model fitting software

I wish to test some model fitting software and I would like to generate synthetic datasets for this test. The synthetic data is supposed to originate from a experiment that measures the change in ...
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0answers
54 views

Optimal Rotation Before Curve Fitting

I am fitting a 1-dimensional polynomial to a set of data points $\{(x_1,y_1,z_1),...,(x_N,y_N,z_N)\} \subset \mathbb{R}^3$ using least squares regression. My first instinct was to choose $x$ as an ...
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0answers
113 views

Bayesian inference and curve fitting

I'm a silly scientist, and I've got a process I'm interested in. It gives me lots of time-series data. I've got an explicit, analytical model that is firmly rooted in reality, and basically boils down ...