skip to main content skip to footer

Illustration of a Test Which Compares Two Parallel Regression Lines When the Variances Are Unequal

Potthoff, Richard F.
Publication Year:
Report Number:
ETS Research Bulletin
Document Type:
Page Count:
Subject/Key Words:
United States Air Force Office of Scientific Research, Hypothesis Testing, Regression (Statistics), Statistical Analysis


In a situation where two regression lines are known to be parallel, it may be desired to test the hypothesis that the two lines are identical without assuming that the variances of the two sets of error terms are necessarily equal. This paper presents a relatively non-technical discussion of a test which can be used for this problem. The test statistic is analogous to the well-known Wilcoxon statistic. The obtaining of the test statistic involves a large number of routine calculations, and (in general) a computer is needed for this. This paper is intended for the practitioner rather than for the theoretician; the more technical aspects of the test are covered in a separate paper (RB-62-30).

Read More