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

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Curve fitting in R

I had 4 groups of data (in color 1 to 4) and one group is the data for one day, so I had 4 days of data. I was trying to fit a line which describes the pattern of theses lines (oscillating pattern) ...
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20 views

Choosing start points for fitting of single and double Gaussian to experimental data

I'm interested in fitting a single and double Gaussian models to some experimental data in matlab. I want to use the amplitude coefficient to detect decreases in the data. I know that the goodness of ...
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11 views

Comparing growth estimates of multigroup growth curve model

I have fitted a growth curve model to describe the trajectories of a variable in 4 groups across three assessment points. I am interested in doing some pair-wise comparisons of the slopes between some ...
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413 views

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 ...
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19 views

what distribution might be a better fit?

I am trying to fit the data (the green curve) with a mixture of normal distribution. I obtained the fitted distribution (the purple curve) from norMixEM(), but the result is not very satisfactory. My ...
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1answer
26 views

Equation of a fitted smooth spline and its analytical derivative

I need to fit a spline function to a data set. I tried with bs, ns and smooth.spline. In my ...
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1answer
23 views

Determining if two growth curves are significantly different

I am developing an artificial model to simulate the growth of two types of biological cells under different conditions. The data I obtained from my model takes the form of two data-sets representing ...
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1answer
107 views

Using the Weibull curve to model responses from a direct mail campaign. Model isn't fitting the data very well

I'm trying to build a model to forecast direct mail marketing campaign responses. In the "response" vector are the average number of responses from a marketing campaign from day 1 to day 63 (8 weeks). ...
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31 views

Associating non-linear three-time-point change with a continuous variable

I would be incredibly grateful for help or advice regarding my following project: I have 3 time points (0, 30, 120 min) and complete data for about $n=500$ subjects for a continuous variable $M$. ...
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80 views

Fit data to a bivariate function

I want to fit my (x,y,z) data points to a function. You can see the data on Fig.1. The data is symmetric along the main diagonal. To understand my data I have studied (y,z) curves at different ...
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27 views

Area under a curve- is there a way to find the % completion of a marketing campaign on a particular day?

I'm trying to build a model to forecast direct mail marketing campaign responses. In the code below I was able to use responses from a previous campaign to create a smooth curve (i.e. continuous ...
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I was able to use R to fit a curve to model direct mail marketing responses- just need the % of responses that are likely to occur each day

I'm trying to model the responses from a direct mail marketing campaign so that I can use it to forecast for future campaigns. In the code below, I started with the average number of responses by day ...
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82 views

How do you find the population size N based on the highest n values?

For example assume $N$ people performed a selection test like GMAT. Assume the distribution of the scores is a normal distribution (but parameters are not known). If you have a list of the $n$ highest ...
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Comparison of two entities based on samples

Suppose I have two sample sets $X = [[x_1, y_1], [x_2, y_2], ...]$ and $Y = [[x_1, y_1], [x_2, y_2], ...]$ data set $x$ points may not the same, also y values change wrt other factors/parameters lets ...
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10 views

Linear fit parameter-errors as a function of the number of data-points

I am trying to work out the errors of $m$ and $b$ in a linear least-square fit of a straight $y = m \cdot x + b$ to $N$ equally-spaced data points $Y_i$ on the interval $I = [-\Delta x \cdot ...
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95 views

Statistical modeling method for curves with uncertainty

I would like to ask for advice on choosing a suitable modelling method for the following problem: I am modeling the performance of a device for curve estimation. I have collected a data set ...
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28 views

How do I interpret which model is the best fit for my distribution (AIC)?

I'm new here so looking for some guidance; How do I interpret the following variables to understanding which model is considered the best fit to my distribution. ...
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2answers
77 views

Curve fitting of (x,y) coordinates

I have three (x,y) coordinates that I got from experimental data. The coordinates represent drug solubility at corresponding pH values as appears below: ...
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270 views

Additive Error or Multiplicative Error?

I'm relatively new to statistics and would appreciate help understanding this better. In my field there is a commonly used model of the form: $$P_t = P_o(V_t)^\alpha$$ When people fit the model to ...
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43 views

Exponential equation fitting

I have two variables: y= head (0.5,0.10,0.15,0.25,0.34) and x= instar (1, 2, 3, 4,5). How fitting my data on exponential growth in R? I need p-value fitting, F (is possible?), R^2 and degree freedom. ...
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1answer
137 views

Using B-splines within a linear mixed-effects model in R

I am using linear mixed-effect model (run with the lme() function in the nlme package in R) that has one fixed effect, one ...
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35 views

Is Linear model right fit here? [duplicate]

I am new to linear regression. I am trying to see if linear curve fitting is the right thing to do here. Here is what I tried. My Data: ...
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1answer
257 views

Fitting a quadratic through 5 points, goal is to find the maximum

I have some physical experiments done at various locations. The locations produces a set of observations y for one value of x, the independent variable. In the end across a set of locations I have ...
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57 views

Curve fitting in R. L-shaped?

I have measurements for my dependent and independent variable across 4 different experimental sites ...
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17 views

R: Fit a trendline to these points in ggplot [duplicate]

I have measurements for my dependent and independent variable across 4 different experimental sites ...
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73 views

Why does matlab show r squared for non-linear

Inspired by the comments here http://stackoverflow.com/questions/27288483/python-multiple-curve-fitting-models In matlab, why is the R squared value displayed if it is meaningless for non-linear ...
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69 views

Fitting a curve best practice

I have some data as tuples $ (y,x)$. I am trying to fit a quadratic curve to the data, its known from the physics of the problem that the relationship should be quadratic. The problem is that I have ...
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Fitting a curve to app retention data

Lets say an app has a retention graph like below (where "1.0" is the number of downloads on october 16, the table is active users, among people who signed up on october 16, on future days). I want to ...
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248 views

Does a best fit make sense in this case?

I have collected data from 60 candidates, 30 female and 30 male, measuring their pain tolerance, or rather time able to withstand pain. I have plotted the times against the $n$th candidate: Would ...
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25 views

Multiple regression for curvilinear seasonal data

This question is related to How to analyze curvilinear seasonal data I have data like following: ...
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99 views

How to analyze curvilinear seasonal data

I have monthly values of a continuous variable from many subjects, the mean of which on plotting show curvilinear pattern with lower values in summer months. How can I analyze and report the ...
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1answer
109 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 ...
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1answer
66 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 ...
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23 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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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 ...
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27 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 ...
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105 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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57 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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114 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
70 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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How should I fit this data?

I have a dataset: ...
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175 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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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, ...
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106 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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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 ...
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1answer
630 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 ...
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64 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 ...
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1answer
66 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) ...
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149 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 ...
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56 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: $\sum_{bin}(f_{data}-f_{model})^2$ ...