Hi I am new to R and statistics and used to linear models. Can you please explain the output? I used it to make a growth curve.

Formula: length ~ a * (1 - exp(-c * est_age))

   Estimate Std. Error t value Pr(>|t|)    
a 1.097e+03  1.026e+01 106.966  < 2e-16 ***
c 1.539e-01  1.982e-02   7.765 2.33e-09 ***
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 

Residual standard error: 41.74 on 38 degrees of freedom
Number of iterations to convergence: 6 
Achieved convergence tolerance: 7.32e-07 
  • 5
    $\begingroup$ Spelling out which R function you used is always good practice. $\endgroup$ – Nick Cox Oct 13 '13 at 11:41
  • $\begingroup$ More information would help. Would you understand the meaning of the column headings if it were a linear regression model rather than a nonlinear model? Would you understand some but not others? $\endgroup$ – Glen_b Oct 14 '13 at 2:26

It appears that you're using nls.

By typing


you can read about the output.

Estimates and standard errors are estimated by the Gauss-Newton algorithm (if the nls defaults are used)

The P-values are the results of a two sided test of whether the parameters are zero or not.

You can check the exact calculations used to create the output shown by typing:

| cite | improve this answer | |
  • 1
    $\begingroup$ Didn't you mean to type "two-sided" instead of "one-sided"? $\endgroup$ – whuber Oct 13 '13 at 16:25
  • $\begingroup$ Yes I did, thanks, well spotted. @whuber, you really pop up everywhere with good responses $\endgroup$ – sqrt Oct 13 '13 at 17:22
  • 2
    $\begingroup$ The model fitted is not logistic. It grows from 0 and approaches an upper asymptote exponentially. $\endgroup$ – Nick Cox Oct 13 '13 at 18:28
  • $\begingroup$ Is it not? I labelled it logistic because it is a specific version of the generalised logistic function $\endgroup$ – sqrt Oct 13 '13 at 18:50
  • 1
    $\begingroup$ Really? A glance at the algebra suggests otherwise. In any case, I'd assert that as usually understood in growth modelling a logistic curve has an inflexion. $\endgroup$ – Nick Cox Oct 13 '13 at 19:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.