  We present measurements of conductance hysteresis on CH3NH3PbI3 perovskite
thin films, performed using the double-wave method, in order to investigate the
possibility of a ferroelectric response. A strong frequency dependence of the
hysteresis is observed in the range of 0.1 Hz to 150 Hz, with a hysteretic
charge density in excess of 1000 {\mu}C/cm2 at frequencies below 0.4 Hz - a
behaviour uncharacteristic of a ferroelectric response. We show that the
observed hysteretic conductance, as well as the presence of a double arc in the
impedance spectroscopy, can be fully explained by the migration of mobile ions
under bias on a timescale of seconds. Our measurements place an upper limit of
approximately 1 {\mu}C/cm2 on any intrinsic frequency-independent polarisation,
ruling out ferroelectricity as the main cause of current-voltage hysteresis and
providing further evidence of the importance of ionic migration in modifying
the efficiency of CH3NH3PbI3 devices.
