Availability of S-ESTREND, a S-PLUSŪ based version of ESTREND

In Reply Refer To:
March 4, 2002
Mail Stop 412

Office of Water Quality Technical Memorandum 2002.12

Subject:  Availability of S-ESTREND, a S-PLUSŪ based version of ESTREND

The purpose of this memo is to announce the availability of S-ESTREND, a
S-PLUSŪ (Insightful Corporation) based version of the computer program ES
timate TREND (ESTREND).  ESTREND is a system of computerized statistical
and graphical procedures for the investigation of trends in water-quality
data.  In its original form (Schertz and others, 1991), ESTREND operated on
a now-obsolete computer platform.  By adapting these packages for 
within S-PLUSŪ, trends in water-quality data can now be analyzed using
state-of-the-art statistical and graphical software.

In addition to its statistical and graphical capabilities, ESTREND
facilitated several operational decisions required in the analysis of
trends at multiple stations.  ESTREND was designed to overcome common
statistical problems encountered by conventional statistical trend
techniques in the analysis of water-quality data.  These problems include
data that are non-normal and seasonally varying and water-quality records
with missing values, censored ("less-than") values, and outliers.
Parametric and nonparametric statistical trend tests were used.  A
nonparametric method, the Seasonal Kendall test, was used for data that had
few censored values or data that were censored at only one reporting level.
The Seasonal Kendall test for uncensored data allowed for the removal of
flow variability in water-quality data.  A parametric test for trend
involving a maximum likely estimation method was used for data that were
censored at multiple reporting levels.

S-ESTREND preserves the functionality of ESTREND and makes it available on
a platform with convenient pull-down menus.  The new software has been
tested extensively, both to ensure consistency of analysis with archived
ESTREND applications and ease of use in new investigations.  On-line help
is included with the software.  Because S-ESTREND duplicates the procedures
documented in Schertz and others (1991), there is no need for additional
formal documentation.  This report is available at:


The software can be downloaded from the USGS NT-TAC Home page:


Note that the user must have installed S-PLUS 2000 and the USGS S-PLUS
library.  Instructions for installing S-ESTREND within S-PLUSŪ are
available at the Internet location given above.

Questions about the S-ESTREND software should be directed to Dave Lorenz (
lorenz@usgs.gov).  Help with S-PLUSŪ can be obtained via email to GS-W help
splus (S-PLUS).


Schertz, T.L., Alexander, R.B, and Ohe, D.J., 1991, The computer program ES
   timate TREND (ESTREND), a system for the detection of trends in
   water-quality data: U.S. Geological Survey Water-Resources
   Investigations Report 91-4040, 63 p.

                                            Stephen K. Sorenson /s/
                                            Acting Chief, Office of Water

This memorandum does not supersede any other Office of Water Quality
Technical Memorandum.

Distribution:  All WRD Employees

(See attached file: (s-estrend02.12)
Stephen K. Sorenson
Acting Chief, Office of Water Quality
US Geological Survey
412 National Center
Reston, VA  20192