VPLX is a FORTRAN 77 program for the calculation of variances for complex sample designs through replication. It is in the public domain. The primary use of VPLX is within the Census Bureau, but it continues to have a number of external users as well.
Two PC versions are available directly from this site. The primary release is for Windows 9x/NT/2000. An earlier Win 3.1 version is also available, but Win 3.1 development has ceased. Both versions are available in executable form, and a Fortran compiler is not required.
A UNIX version is available in the form of Fortran source code. A SUN/Solaris version of the executable is also offered. If the executable is not compatible with the user's system, a Fortran compiler (f77 or f90) will be required to install VPLX.
VPLX evolved within an original syntactic design. To improve the usability of VPLX, a three-phase plan to improve the syntax began in 1997. Version 1998.09 reflects the results of the first phase of revision. It has received considerable internal testing at the Census Bureau, and it is now the primary production release. The site now emphasizes this version. A beta version from the second phase is currently being tested internally, and it will be posted here when released.
The revisions are designed to maintain upward compatibility, so that new versions will continue to run legacy applications.
VPLX is written in FORTRAN 77, but users are not required to know Fortran. Instead, users specify the application in the VPLX language.
Currently, the VPLX language is undergoing major revision. For example, the following sample of old syntax,
subtract persons minus rooms into test if test (1-high) then _ constant 1 into overcrowded end if
is equivalent to the following new syntax,
if persons > rooms then overcrowded = 1;
As this example illustrates, the new syntax incorporates features of Fortran, the SAS language, and other computationally oriented languages.
VPLX applications are organized into a series of steps. The new syntax has been implemented in the CREATE step and the closely related REWEIGHT step. The current production version of VPLX, 1998.09, incorporates these revisions. Version 1998.09 also runs applications with CREATE or REWEIGHT steps written in the old syntax. Thus, this version is recommended to all users except PC users running Windows 3.1.
A beta version is currently undergoing testing at the Census Bureau. It incorporates revised syntax for the TRANSFORM step. It will also support older applications.
Consequently, all but Windows 3.1 users are currently encouraged to work with the production release.
VPLX has also been compiled under VAX VMS and some other environments, but only PC and UNIX versions are currently maintained on this site.