Quality & Quantity 36: 145–167, 2002.
© 2002 Kluwer Academic Publishers. Printed in the Netherlands.
Multi-Method Triangulation in a Qualitative Study
on Teachers’ Practical Knowledge: An Attempt to
Increase Internal Validity
PAULIEN C. MEIJER, NICO VERLOOP and DOUWE BEIJAARD
Leiden University, ICLON Graduate School of Education, P.O. Box 9555, 2300 RB Leiden, The
Netherlands. E-mail: MeijerP@iclon.leidenuniv.nl
Abstract. This article describes multi-method triangulation as a means to enhance the internal valid-
ity in a qualitative study on language teachers’ practical knowledge. Teachers’ practical knowledge
is viewed as a multi-dimensional concept, requiring multiple instruments for its exploration. In the
triangulation procedure, data collected with three instruments were analysed and related to each
other. Three steps of analysis, preceded by a pre-analysis step, were used to combine these data. The
triangulation procedure culminated in a fairly comprehensive understanding of teachers’ practical
knowledge with respect to the teaching of reading comprehension to 16- to 18-year-old students.
It was concluded that multi-method triangulation is a worthwhile procedure to enhance the internal
validity in qualitative studies on a complex topic such as teachers’ practical knowledge.
Key words: triangulation, qualitative research, research methodology, education, educational re-
1. Triangulation in Qualitative Research
Now that qualitative research has established its own place in research on teaching
(Silverman, 1997), the quest for more sophisticated procedures to secure objectiv-
ity in this type of research is increasing (e.g., Miles and Huberman, 1994). Two
critical issues in regard to objectivity are reliability and validity. This article spe-
ciﬁcally deals with enhancing the internal validity of qualitative research. This is
done in the context of a study about teachers’ practical knowledge. In conceptual-
izing “internal validity”, we follow Miles and Huberman (1994), who stated that
internal validity has to do with questions such as “Do the ﬁndings of the study
make sense?, Are they credible to the people we study and to our readers?, Do we
have an authentic portrait of what we were looking at?” (p. 278). Pedhazur and
Pedhazur-Schmelkin (1991) described internal validity, though in the context of
(non)experimental research, as the sine qua non of meaningful research.
Gliner (1994) described triangulation as a method of highest priority in de-
termining internal validity in qualitative research. Triangulation is a concept that
originated in the discipline within the ﬁeld of geography concerned with land sur-