  We present new spectroscopic data for twenty six stars in the
recently-discovered Canes Venatici I (CVnI) dwarf spheroidal galaxy. We use
these data to investigate the recent claim of the presence of two dynamically
inconsistent stellar populations in this system (Ibata et al., 2006). We do not
find evidence for kinematically distinct populations in our sample and we are
able to obtain a mass estimate for CVnI that is consistent with all available
data, including previously published data. We discuss possible differences
between our sample and the earlier data set and study the general detectability
of sub-populations in small kinematic samples. We conclude that in the absence
of supporting observational evidence (for example, metallicity gradients),
sub-populations in small kinematic samples (typically fewer than 100 stars)
should be treated with extreme caution, as their detection depends on multiple
parameters and rarely produces a signal at the 3sigma confidence level. It is
therefore essential to determine explicitly the statistical significance of any
suggested sub-population.
