gompertz

  1. S

    Formula for S shaped curve given specific values

    I need to derive a formula that will give me an S-shaped curve, such as this one: The x-values would go from 0 to 250 and the y-values from 0 to 50. After searching I found this to be a sigmoid function or logistic function, but to be honest, my level of knowledge isn't high enough to...
  2. @

    summing two probability density functions---Gompertz hazard model?

    Hi, r-help members. I have a question about summing two density distributions. I have two samples from which I've estimated hazard parameters for a Gompertz mortality model. With those parameters, I can calculate the PDF (survival function times hazard function) of ages-at-death in a birth...
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    log-rank (or other) test for difference between survival curves

    Hi, all. I have co-opted some R code that estimates parameters for a Gompertz-Makeham mortality model. The data to which the model is fit is interval censored, with counts of individuals in each age-range category. For example: naga <-...
  4. Q

    grofit package model validation

    Hello, I used the grofit package (gcFitModel) for my data and obtained values for A, mu, and lambda. Its possible to easily do a cor.test for my observed data and the parameter I get for A (asymptotic size), but I am unable to figure out how to validate either all my parameters at once, or...
  5. Q

    Gomperz growth curve with grofit package

    Hi, I used the grofit package in R to fit the Gompertz growth model to my data (growth of quails over the course of several weeks). I obtained results for the three separate parameters: A, mu, and lambda. My main question is: is it possible to have negative values for lambda (lag phase)? It...