Banner for LabNotes
From Lab Notes
Contact Information
Forest Products Laboratory
One Gifford Pinchot Drive
Madison, WI 53726-2398
Phone: (608) 231-9200
Fax: (608) 231-9592


You are here: FPL Home  / Information Products & Services  / Publications

Requested Product

Title: Simulations of nonparametric analyses of predictor sort (matched specimens) data

Source: Res. Pap. FPL-RP-699. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory: 1-83.

Author(s)Verrill, Steve P.; Kretschmann, David E.

Publication Year: 2019  View PDF »

Category: Research Papers
Associated Research Project(s):   FPL-4714-1B  FPL-4851-2B

Abstract: A type of blocked experiment has the potential of being poorly designed and analyzed. Several papers by Verrill and co-workers referred to such an experiment as a “predictor sort” experiment. It has also been referred to in other papers and textbooks as “artificial pairing” and “matched pair” or “matched subjects” design. The associated design process is also sometimes described as “forming blocks via a concomitant variable.” In a wood research context, the response in such an experiment might be lumber strength after a treatment, and the predictor used to form blocks would be some combination of lumber stiffness, knot size, and slope of grain (all of which can be measured nondestructively prior to specimen allocation). Improperly designed or analyzed, predictor sort experiments can be associated with incorrect power calculations, inappropriate sample sizes, incorrect tests of hypotheses, and incorrect confidence intervals. In a 2017 paper, Verrill and Kretschmann reviewed the main results in the literature, added a section on multiple comparisons, and presented the results from power and confidence interval coverage simulations that emphasized the importance of proper design and analysis of predictor sort experiments; that work was based on the assumption that the predictor and the response have a bivariate normal distribution. This paper, which can be thought of as a companion to the 2017 paper, constitutes a nontheoretical, simulation-based first look at the effect of predictor sort allocation on nonparametric hypothesis tests (Kruskal–Wallis, one-way on ranks, oneway on Van der Waerden ranks, two-way on ranks, and Friedman tests) and nonparametric confidence bounds on quantiles. It also considers situations in which a bivariate normal assumption for the predictor–response pair does not hold.

Keywords: Predictor sort sampling; artificial pairing; matched pairs; matched subjects; concomitant variable; blocked ANOVA; analysis of covariance; nonparametrics; confidence bounds on quantiles

Publication Review Process: Informally Refereed (Peer-Reviewed)

File size: 1,024 kb(s)

Date posted: 09/05/2019

This publication is also viewable on Treesearch:  view
RITS Product ID: 94910
Current FPL Scientists associated with this product (listed alphabetically)
Kretschmann, David E.
Research General Engineer
Verrill, Steve P.
Mathematical Statistician

Additional items that might interest you
View the video celebrating FPL's 100 years of public service in 2010, from the producers of the Greatest Good....view

Research Highlights from FPL....view

Termite Eradication: A search for the Holy Grail.... view

Moisture Management in Residential Construction Series videos...view

Wood Floor Systems in Residential Construction Series videos....view
- FPL's Mission and Strategic Plan -

FPL's mission is to identify and conduct innovative wood and fiber utilization research that contributes to conservation and productivity of the forest resource, thereby sustaining forests, the economy, and quality of life. ... ..more »

- FPL Research Emphasis Areas -
Advanced Composites

As an integral part of the FPL mission, we improve the long-term sustainability of our Nation's forests by creating valuable composite products from biobased materials ... ..more »

Advanced Structures

The FPL has been in the forefront of wood-frame housing research since 1910 and has long been recognized as a world leader in such housing-related areas as engineered wood ... ..more »

Forest Biorefinery

We all know the compelling reasons that the United States needs to reduce its dependence on fossil fuels. Historically, the greatest increases in energy demand have been for transportation fuels ... ..more »


A leader in wood products research for over a century, the FPL is positioning itself to become the lead Federal research facility for the application of nanotechnology in forest products ... more »

Woody Biomass Utilization

Forests in the United States contain a substantial amount of small-diameter, overstocked, and underutilized material.FPL research projects are exploring the potential of the small-diameter ... ..more »