# Questions tagged [logistic-curve]

A common S-shaped ("sigmoid") curve, defined as $f(x) = L/(1+e^{-k(x-x_0)})$.

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### What is worst than a random, in ROC then say lower-right space is worst than random

Nothing can be worst than random, if you are predicting wrong all the time then why don't you just invert your results all the time and then you will be in the upper-left area of the ROC curve i.e. ...
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### What is the interpretation of the “C” parameter in the five parameters logistic curve?

I'm using the following equation for the 5-parameters logistic curve: $$y = A + \frac{D-A}{\Bigl(1+\exp\bigl(B(C-x)\bigr)\Bigr)^S}$$ What is the interpretation of the $C$ parameter? I found some ...
57 views

### Generate odds ratios across deciles / quantiles of an indpendent variable

With reference to the following figure from Bellomo et al., 2011: How exactly are the odds ratios across the deciles 'referenced against the 4th decile' calculated? My initial impression is that a ...
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### How to calculate an index value between 1 and 0 for distance, based on a logistic function

I work with spatial ecology, and have calculated distances from one island to its neighboring islands. I want to transform these distances to index values between 0 and 1, where the closest islands ...
224 views

2k views

### Adjusting S-Curves (Sigmoid Functions) with Hyperparameters

I can define the sigmoid function in R with: ...
169 views

### How to analyse growth rate in R?

Within the framework of an experiment I followed to growth rate of bird nestlings. I measured them every day for weight and tarsus. I have a number of continuous and categorical explanatory variables, ...
1k views

### Fitting a dose response curve to 3 dose points

I have dose-response data sets, of 3 doses, 3 replicates for each dose. I'd like to fit a curve for these data sets and I'm mainly interested in the slope of the curve since I want to be able and ...
330 views

### (How) Can I fit a dataset with some parameters fit globally?

I want to fit some sigmoidal curves that follow the following equation: bottom+(top-bottom)/(1+10**((logIC50-x)*HillSlope)) the parameters top and bottom should ...
505 views

### Automatically finding starting values for a sigmoid curve

I have ~10.000 of vectors and I want to fit a sigmoid curve to each of them; in each case, I need to define starting parameters for fitting, so I want to find these parameters automatically. On ...
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### Looking for function to fit sigmoid-like curve

I'm looking for a function to fit sigmoid-like curves, from experimental data points. The model (the function) doesn't matter, it doesn't have to be physically relevant, I just want to be able to ...
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### Why is the logistic distribution called “logistic”?

What is "logistic" about the logistic distribution, in a common sense way? What is the etymology of and the lexical rationale for the name, not just pure math definition?
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### 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 'non-forest'....
183 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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### 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 ...
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### Estimating the slope of the straight portion of a sigmoid curve

I have been given this task and was stumped. A colleague asked me to estimate the $x_{upper}$ and $x_{lower}$ of the following chart: The curve is actually a cumulative distribution, and x is some ...