Statistical Analysis Stack Exchange
Statistical Analysis Stack Exchange

Questions tagged [curve-fitting]

Methods used to fit curves (as in linear or non-linear regression) to data.

588 questions
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Data has two trends; how to extract independent trendlines?

I have a set of data that is not ordered in any particular way but when plotted clearly has two distinct trends. A simple linear regression would not really be adequate here because of the clear distinction between the two series. Is there a simple…
jonathanbsyd
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What does negative R-squared mean?

Let's say I have some data, and then I fit the data with a model (a non-linear regression). Then I calculate the R-squared ($R^2$). When R-squared is negative, what does that mean? Does that mean my model is bad? I know the range of $R^2$ can be…
RockTheStar
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Interpreting the difference between lognormal and power law distribution (network degree distribution)

First off, I'm not a statistician. However, I have been doing statistical network analysis for my PhD. As part of the network analysis, I plotted a Complementary Cumulative Distribution Function (CCDF) of network degrees. What I found was that,…
Mike
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What's the most pain-free way to fit logistic growth curves in R?

This isn't as easy to Google as some other things as, to be clear, I'm not talking about logistic regression in the sense of using regression to predict categorical variables. I'm talking about fitting a logistic growth curve to given data points.…
readyready15728
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New revolutionary way of data mining?

The following excerpt is from Schwager's Hedge Fund Market Wizzards (May 2012), an interview with the consistently successful hedge fund manager Jaffray Woodriff: To the question: "What are some of the worst errors people make in data mining?": A…
vonjd
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How do I interpret the covariance matrix from a curve fit?

I'm not too great at statistics, so apologies if this is a simplistic question. I am fitting a curve to some data, and sometimes my data best fits a negative exponential in the form $a * e^{(-b * x)} + c$, and sometimes the fit is closer to $a *…
Jason Martens
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Is there a formula for an s-shaped curve with domain and range [0,1]?

Basically I want to convert similarity measures into weights which are used as predictors. The similarities will be on [0,1], and I will restrict the weights to also be on [0,1]. I'd like a parametric function that does this mapping which I'll…
user117053
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Anscombe-like datasets with the same box and whiskers plot (mean/std/median/MAD/min/max)

EDIT: As this question has been inflated, a summary: finding different meaningful and interpretable datasets with the same mixed statistics (mean, median, midrange and their associated dispersions, and regression). The Anscombe quartet (see Purpose…
Laurent Duval
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Difference between regression analysis and curve fitting

Can anybody please explain to me the real difference(s) between regression analysis and curve fitting (linear and nonlinear), with an example if possible? It seems that both try to find a relationship between two variables (dependent vs independent)…
Ali Sultan
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Determining best fitting curve fitting function out of linear, exponential, and logarithmic functions

Context: From a question on Mathematics Stack Exchange (Can I build a program), someone has a set of $x-y$ points, and wants to fit a curve to it, linear, exponential or logarithmic. The usual method is to start by choosing one of these (which…
Mitch
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What kind of curve (or model) should I fit to my percentage data?

I am trying to create a figure which shows the relationship between viral copies and genome coverage (GCC). This is what my data looks like: At first, I just plotted a linear regression but my supervisors told me that was incorrect, and to try a…
teaelleceecee
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Why are there large coefficents for higher-order polynomial

In Bishop's book on machine learning, it discusses the problem of curve-fitting a polynomial function to a set of data points. Let M be the order of the polynomial fitted. It states as that We see that, as M increases, the magnitude of the…
Abhishek Bhatia
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LOESS that allows discontinuities

Is there a modelling technique like LOESS that allows for zero, one, or more discontinuities, where the timing of the discontinuities are not known apriori? If a technique exists, is there an existing implementation in R?
Jeromy Anglim
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How to fit a Weibull distribution to input data containing zeroes?

I'm trying to reproduce an existing prediction algorithm, handed down by a retired researcher. The first step is to fit some observed data to a Weibull distribution, to obtain a shape and scale which will be used for predicting future values. I'm…
Ethan Shepherd
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How can I programmatically detect segments of a data series to fit with different curves?

Are there any documented algorithms to separate sections of a given dataset into different curves of best fit? For example, most humans looking at this chart of data would readily divide it into 3 parts: a sinusoidal segment, a linear segment, and…
whybird
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