Quality & Quantity 35: 191–202, 2001.
© 2001 Kluwer Academic Publishers. Printed in the Netherlands.
Effects of Using Mean Scores in Regression
Models: An Example From Environmental
C. CAMACHO MTZ-VARA DE REY, M. P. GALINDO GALINDO and M. A.
Departamento de Psicología Experimental, Facultad de Psicología, Universidad de Sevilla, Avda.
San Francisco Javier, s/n. 41005 Sevilla
Abstract. Multiple regression analysis with grouped data is often used as a method for exploring
environmental preferences, the preferred unit for measurement in such analyses is mean scores rather
than individual scores.
Although this procedure allows us to reduce the potential for error in measuring different vari-
ables and, as a consequence of this, improves the reliability of the technique, it also produces some
additional, undesirable effects. The latter include artiﬁcial increases in R
values which give the
impression that a high degree of ﬁt has been achieved for the regression model. Indeed, this goodness
ﬁt often appears to be better than that which could have been achieved by using individual scores.
Further, given that different studies operate with differing numbers of subjects in their groups, the
scores which result from the analyses of these groups are not directly comparable.
In the following discussion, we demonstrate how any value, other than zero for correlations
between variables, can be increased, at will, by simply expanding the number of subjects in each
group. We present the specialised formulae used for quantifying this increase and offer a warning
about the purely relative nature of any study which bases its conclusions on models of regression
analysis using grouped data.
Key words: environmental psychology, environmental preferences, multiple regression
One of the more popular strands of research in Environmental Psychology which
has emerged in the last few years is that of environmental choice or the en-
vironmental preferences which individuals express. By examining the subjective
judgements of individuals these studies attempt to develop a proﬁle of those par-
ticular environmental characteristics which are most pleasing to the individual.
These studies attempt to isolate those environmental attributes which are positively
valued by subjects, and increase the numbers of these elements in the resulting
environmental design. In this way such studies aim at increasing the environmental
quality of a given area.