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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...
View ArticleComparing 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...
View ArticleR-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...
View ArticleFitting known equation to data
I have measured growth rates over a range of temperatures (temperature response curve) and would like to fit an already established equation/model to it. I’m very new to R and have trouble coding it...
View ArticleCurve fitting and analytical solutions vs kernel density estimation and sampling
I have some data, and I want to find the expected value of the maximum of $n$ samples of this data. What of the following methods would typically get me the best results? Visually inspect the...
View ArticleAveraging Cumulative Distribution Function
I have several (x,y) datasets which form various CDF curves. These are generated by cross-validating models built with different parameters. For example: Aa = [0, 0.1 1, 0.2, 2, 0.3, ... xn, yn] Ab =...
View ArticleWhat 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...
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How to fit a curve for a histogram [closed]
I am trying to fit a curve (gaussian) for my distribution represented here with an histogram, like the red curve represented in the attached shema. X = rchisq(1000, df = 5) hist(X) Thank you
View ArticleDeciding between linear and non-linear fits [on hold]
I’m basically trying to calculate the pollution level of water bodies. I have a data set (~3,500 points) of pH values of a particular lake from 2005-15. As pH itself is a logarithmic scale but there’s...
View ArticleJustification by enhancement of $R^2$
Is (great) enhancement of $R^2$ sufficient to justify the use of another model ? other desciptives variables ?
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