Gomperz growth curve with grofit package

#1
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 seems a bit strange to me, but when I fit my data to the model it gave an "ok" for the fit... so I assumed it was correct, but I cant find much of anything in the literature about the lag phase interpretation (especially if they have negative values, or if negative values are even possible and/or biologically relevant). Any help or insight would be greatly appreciated. Thank you.
 

Mikko

New Member
#2
I am not familiar with grofit package, but by looking at the function lambda seems to be equivalent to t0, which is used in another package. This is a modelling artifact that is said to present the age when the average length is zero. Thus there should be no problem even though it's negative. Your observations are probably well over zero and this leads to negative lambda.

EDIT: You gotta be careful when trying to find biological meaning for these modelling parameters. You may use them to compare populations, but some of them, such as this lambda, have little meaning otherwise.
 
#3
Dear Grofit User,

I am new grofit user. I am biotechnologist and hence no good experience in grofit. Can anybody tell me for which grofit function should I use for creating graph for effect of different concentration of salts on growth of bacteria.
I want to know maximum growth (A), slope (mu), lag phase (lambda) all.

for example I did experiment with 0.25M NaCl concentration and I took OD600 at 12, 24, 36, 48, 60, 72, 84, 96 hrs.
I want to know how to put these values when using grofit package to obtain the graph.
If possible please explain from starting because I am new user and have no background in it.
Try to make it as simpler as possible

Looking forward to receive response from grofit user.

Thanks in advance
Grofit