A computer program for estimating the Gompertz curve,
using Gauss-Newton method of least squares, is described in
this article. The program is developed using Scilab (Version
3.1.1), a freely available scientific software package that can
be downloaded from www.scilab.org. Data is to be fed into
the program from an external disk file which should be in the
MS-Excel format. The output will contain a list of initial as well
as final estimates of the parameters, standard errors; value of
Gauss-Normal equations namely GN1, GN2 and GN3; number
of iterations; variance (σ2); goodness of fit measures such as
R2; Durbin-Watson statistic (DW); D-value, where
covariance matrix; and residuals.
It also displays a graphical output of the estimated curve vis-a-vis
the observed curve.
Despite the diversity of available statistical software packages such as SAS, SPSS, SYSTAT,
PASS, and there is a shortage of stand-alone programs that allow users to estimate the
parameters of Gompertz curve using the Gauss-Newton method of least squares.
SPSS 12.0 and SYSTAT 11.0 do not provide any Gompertz growth models in their software
package. However, SAS 9.1 does provide a programming interface to develop a program
for Gompertz growth models using the Gauss-Newton method of least squares; but it
is not very user-friendly. PASS provides users with a modified Gompertz growth model
but the method for estimating the parameters of Gompertz curve cannot be specified
by the user.
This paper documents a computer program for estimating the parameters of
Gompertz curve using the Gauss-Newton method of least squares.
The program is written in Scilab (Version 3.1.1) and is run on a desktop PC with
a Pentium IV processor and 256 KB of RAM. Scilab is a scientific software package
to develop programs that requires numerical computations. It provides a powerful
open computing environment for engineering and scientific applications. Developed
since 1990 by researchers from INRIA and ENPC, it is now maintained and developed
by Scilab Consortium since its creation in May, 2003. It is distributed freely and open
source, via Internet since 1994, and is currently being used in educational and
industrial environments around the world. It can be downloaded freely from
www.scilab.org |
