  FRBs are a newly discovered class of extragalactic radio transients
characterised by their high energy and short-duration (~$\mu$s-ms)[1]. Their
elusive physical origin remains a subject of ongoing research, with magnetars
emerging as leading candidates[2],[3]. Previous studies have employed various
methodologies to address the FRB origin problem, including demographic analyses
of FRB host galaxies and their local environments[4]-[6], assessments of FRB
rate evolution with redshift[7]-[9], and searches for proposed multi-messenger
FRB counterparts[10]. However, these studies are susceptible to significant
biases stemming from unaccounted radio and optical selection effects. Here we
present empirical evidence for a substantial selection bias against detecting
FRBs in galaxies with large inclination angles (edge-on) using a sample of
hosts identified for FRBs discovered by untargeted surveys. This
inclination-related bias likely leads to a significant underestimation (by
about a factor of two) of the FRB rates reported in the literature and
disfavours globular clusters as the dominant origin of FRB sources, as
previously speculated[6]. These conclusions have important implications for FRB
progenitor models and targeted FRB follow-up strategies. We further investigate
the impact of this bias on the relative rate of FRBs in different host
environments. Our analysis suggests that scattering in FRB hosts is likely
responsible for the observed bias[11],[12]. However, a larger sample of
localised FRBs is required to robustly quantify its contribution in the
inclination-related selection bias.
