The dangers of being trigger--happy
  We examine the evidence offered for triggered star formation against the
backdrop provided by recent numerical simulations of feedback from massive
stars at or below giant molecular cloud sizescales. We compile a catalogue of
sixty--seven observational papers, mostly published over the last decade, and
examine the signposts most commonly used to infer the presence of triggered
star formation. We then determine how well these signposts perform in a recent
suite of hydrodynamic simulations of star formation including feedback from
O--type stars performed by Dale et al (2012a, b, 2013a, b, 2014). We find that
none of the observational markers improve the chances of correctly identifying
a given star as triggered by more than factors of two at most. This limits the
fidelity of these techniques in interpreting star formation histories. We
therefore urge caution in interpreting observations of star formation near
feedback--driven structures in terms of triggering.
