[en] Gamma-ray bursts (GRBs) are brief bursts of high-energy electromagnetic radiation originating from space, formed in an ultra-relativistic jet produced in the aftermath of a newly born stellar mass black hole. A subclass of so-called long-duration GRBs (LGRBs, lasting typically a few tens of seconds) have been shown to be associated with the core-collapse of massive stars. Due to the short-lived nature of massive stars, LGRBs have been suggested as promising tracers of star formation up to the earliest epochs of the Universe. However, not all massive star core-collapses give rise to LGRBs as these are rare events, requiring particular conditions to form. In this thesis, we investigate a crucial ingredient for using LGRBs as tracers of star formation: the LGRB efficiency, defined as the fraction of core-collapses that form an LGRB. In the first part of the thesis, we present a statistical population model developed to reproduce three carefully selected observational constraints. This model allows us to constrain the intrinsic LGRB population and quantify the LGRB efficiency, showing that it increases with redshift. The second part of the thesis is devoted to identifying the factors affecting the LGRB efficiency by studying a complete, unbiased sample of LGRBs at 1 < z < 2. We study the environments in which LGRBs form by studying the properties of their host galaxies and comparing them with typical star-forming galaxies. We show that, as expected from theoretical considerations, metallicity is a key driving factor behind the LGRB efficiency. These results combined bring us one step closer to understanding the progenitors of LGRBs. (author)