Introduction

Statistics is nowadays often referred to as data science. Today’s data are much bigger, and more complex, than what a statistician had to handle decades ago; hence, not surprisingly, today’s statistical models are also much more complex. From a classical i.i.d. (independent and identically distributed) model to a linear regression model; from a linear regression model to a linear mixed model; and from a linear mixed model to a nonlinear mixed effects model, we are witnessing an ever-changing story about our data, in good ways.