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

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Curve registration for plots with significant fluctuations [on hold]

I am doing some stuff about functional data analysis, but I come across some trouble when I try to analyze curves with significant fluctuations. I use the sample data "StatSciChinese" in "fda" ...
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7 views

Calculating the confidence interval of a curve fitted through data points each with a confidence interval itself

I have a number of data points, (x,y), where both variables represents a measured quantity each with a confidence interval. These variables correlate strongly with each other. I want to fit a curve ...
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27 views

Best way to model this data, qfit or fpfit? How to get equation?

So I have this relationship, which is obviously not linear. The purpose is to see if there is (and what kind of) a relationship between FRAG (test score) and MD-R (mm^2/s). There are other covariates ...
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1answer
41 views

Fitting an arc from samples taken at evenly spaced angles

I have an application where I am rotating an object and measuring its position in X,Y as it rotates. There is some measurement error in both X and Y at each point (haven't yet been able to ...
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27 views

How to find (using R) the function which my experimental data follow?

I have an experimental time-depending data (Mean as a function of Time). I want to find the function which my data follow. I have already tried fitdistr and Gam, but it hasn't really helped. Could ...
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34 views

Finding the best fitted distribution for an experimental data with R

I have read most of the similar questions and answers, but still can not solve my problem... I have an experimental medical time-depending data, which I want to analyse and classify. I'm trying to ...
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10 views

Fitting distributions to multi dimensional data

I have a set of data with losses are dependent variable. It also has 2 independent variables such as location and type of injury. For each location and injury type combination, I need to fit a ...
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1answer
23 views

Fitting curves to means and variances from multiple samples

I have data on a variable measured in multiple longitudinal samples. I do not have the individual-level data for each sample, just the sample means and variances at each time point. The samples do not ...
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37 views

How to show fitting line in the data tested with Spearman's rank order correlation?

Above is the scatter plot of my data. The spearman's rho was 0.66 which was significant (p<0.005). I draw the fitting line using polynomials. My question: is it OK to choose arbitrary function ...
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6 views

Given ROI data what should I use as the coefficients in a sigmoid curve?

I've got a bunch of marketing data : total spend, adstock decay rates, incremental volume, cost of media metric, campaign length, Return On Investment which would I use as the parameters of an ...
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34 views

How can we use genetic algorithm for curve fitting?

I want to use genetic algorithm in order to fit a curve to some data, or in other words, to estimate some equation that describes the relationship. Suppose that I select the equation to be a ...
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18 views

Evaluation of curve fitting

I have 10 different curves, and the curves are on different ranges. For example, curve 1 has range [-1,1], curve 2 has range [-10,10], etc. Now based on my model, I get one estimated curve for each ...
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266 views

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 ...
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82 views

Fitting the differences between two curves

The problem I'm trying to solve is to algorithmically figure out whether two curves converge or diverge in a graph (visually the problem is almost trivial). For examples: The left one is ...
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48 views

What polynomial do I need for regression of such relations

I have following 4 graphs and for each I have to do regression. The relation is clearly curvilinear. What term should I use for regression (eg y ~ x+x^2) for each of these?
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29 views

What equation should I fit to this plot? (similar to double exponential?)

I have data that looks somewhat like the following plot (and dataset). It's been suggested that a double exponential (e.g. k (exp(−αt) − exp(−βt))) might fit it, but I can seem to get it to fit (using ...
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53 views

Using Bayesian inference to fit functions

I'm trying to understand Bayes Inference better and was wondering if it is possible to use it to fit a function $f(t)$ where I only know the value $f(t)$ for a few values of $t$. For each value of $t$ ...
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82 views

R-squared as criterion to choose between linear and non-linear regression

I am working in some regression models to forecast opinions based on general demographic characteristics, and I'm not sure how to choose between linear regression and curve estimation (I'm using SPSS ...
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74 views

find a general formula between two parameters using curve-fit

I am trying to study the relationship between two parameters say A and B for an image. For a single scene S1, I take 20 images ...
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66 views

fitting parametric survival curves on Kaplan Meier probabilities in aggregate data

Lets suppose I have aggregate survival probabilities (NOT individual level data) from Kaplan Meier curves. I would like to curve fit different "types" of distribution like exponential, weibull, ...
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82 views

Calculate prediction values for linear curve estimation for next 5 intervals

Below is my code with sample data as in screen shot ; in that i got response for only 21 to 33. My requirement is to get response for 34, 35 , 36, 37 Sample Data Below is R code ...
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39 views

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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54 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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25 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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495 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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21 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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124 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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46 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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145 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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33 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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90 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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36 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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55 views

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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87 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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9 views

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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14 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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99 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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30 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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108 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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501 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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62 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
223 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
284 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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66 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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18 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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115 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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73 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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19 views

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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257 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 ...