What do gas-rich galaxies actually tell us about modified Newtonian
  dynamics?
  It has recently been claimed that measurements of the baryonic Tully-Fisher
relation (BTFR), a power-law relationship between the observed baryonic masses
and outer rotation velocities of galaxies, support the predictions of modified
Newtonian dynamics for the slope and scatter in the relation, while challenging
the cold dark matter (CDM) paradigm. We investigate these claims, and find
that: 1) the scatter in the data used to determine the BTFR is in conflict with
observational uncertainties on the data; 2) these data do not make strong
distinctions regarding the best-fit BTFR parameters; 3) the literature contains
a wide variety of measurements of the BTFR, many of which are discrepant with
the recent results; and 4) the claimed CDM "prediction" for the BTFR is a gross
oversimplification of the complex galaxy-scale physics involved. We conclude
that the BTFR is currently untrustworthy as a test of CDM.
