  The partial least squares (PLS) is a popular modeling technique commonly used
in social sciences. The traditional PLS algorithm deals with variables measured
on interval scales while data are often collected on ordinal scales: a
reformulation of the algorithm, named ordinal PLS (OPLS), is introduced, which
properly deals with ordinal variables. An application to customer satisfaction
data and some simulations are also presented. The technique seems to perform
better than the traditional PLS when the number of categories of the items in
the questionnaire is small (4 or 5) which is typical in the most common
practical situations.
