The core content of this book was written 20 years ago, when I began giving my first courses on structural equation modeling at the François Rabelais University in Tours, France. Having never been left pending, the manuscript has been constantly updated for the needs of my university courses and numerous introductory workshops to SEM that I was conducting in various foreign universities. These courses and workshops were both an introduction to the statistical tool and an adoption of a software without which this tool would be obscure, abstract and disembodied. To put it directly and bluntly, any introduction to structural equation modeling (SEM) compulsorily includes adopting a SEM software. Among LISREL, Amos, EQS, Mplus Sepath/Statistica, and Calis/SAS, there is no dearth of options. These commercial programs no doubt helped in demystifying structural equation modeling and have thus given it an actual popularity that continues to grow.
Writing a book, in this case a practical handbook of structural equation modeling, requires introducing one or more of these commercial software that are admittedly quite expensive. That is where the problem lies. Not that they do not deserve it, but picking one is inevitably advertising that software. I cannot and will not consent to this. Moreover, access to these commercial software remains, for many students and young researchers, an obstacle and constraint that is often insurmountable. I have often experienced the challenge of teaching SEM in African universities where it was impossible to have SEM commercial software. I happened to use a restricted student version of a commercial program to demonstrate in my class.
When R, free open-source software, was developed, the situation changed. R is made of packages dedicated to all kinds of data analysis and processing. The lavaan package, provided by Rosseel [ROS 12], is dedicated to SEM. It achieved immediate success as it has all the features proposed by commercial software, and it offers such a disconcerting ease of use. As with any statistical tool, practice remains the best way to master SEM. There is no better way to do this than by having software at hand. R and lavaan have changed our way of teaching statistical tools as well as the way in which students can become familiarized with, adapt, and use them. Our level of demand on them changes as the students' view of these tools evolves. Understanding, learning, and especially practicing without any limits (apart from that of having a computer): this is what R and its lavaan package offer to students. This book certainly contributes to it.
Without the impetus and the decisive and meaningful contribution of Guillaume Broc, author of the book Stats faciles avec R (De Boeck), this manual would not have seen the light of day. We share the following belief: access to science and its tools must become popular and be available to everyone. We think that this manual, devoted to structural equation modeling with lavaan, fully contributes to this purpose.
It is because this book aims to be a didactic handbook and a practical introduction to SEM meant for students and users who do not necessarily need complex mathematical formulae to adopt this tool and be able to use it wisely, that we submitted the first draft to some novice students in SEM in order to assess its clarity and comprehensibility. Their careful reading and their judicious and pertinent comments allowed for a substantial improvement of this manual. They are very much thanked for this. In fact, they are fully involved in this project. However, we retain and accept full responsibility for mistakes, shortcomings, or inadequacies that may be present in this manual.
Kamel GANA
October 2018