had different cuts been applied. Higher cuts make little difference, but lower cuts raise the likelihood of high values of $\alpha$. For example had the same distribution of $V_r/\sigma$ been observed for cuts as low as low as $V_{min}=30$[kms$^{-1}$]{} and $V_{min}=15$[kms$^{-1}$]{}, for the NIRSPEC and ISAAC datasets, the data would be consistent with the massive-halo model, with $p=0.15$. This may be understood by reference to Figure \[fig:lbg\_cumf\]. Higher values of $V_{min}$ raise the low–end cut off of the predicted curve of $V_r/\sigma$. High values of $\alpha$ are ruled out once the tail passes the fist point on the stepped line. Lowering the cuts extends the tail of the curve to smaller values of $V_r/\sigma$, so that larger values of $\alpha$ are permitted. This illustrates the importance of specifying well–defined selection criteria.

Discussion {#sec:lbg_discussion}
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To summarise the previous section, we have improved on our earlier dynamical estimate of the virial masses of the haloes of LBGs at redshift $z=3$, by accounting for the effects of seeing, slit width, and observational uncertainties. From an analysis of the small number of available rotation curves for LBGs we determined a relation $V_{c7}=(1.9\pm0.2)\sigma$. We used this to transform the measured velocity widths of 32 