The lower hybrid current drive efficiency of 66 Tore Supra pulses has been investigated. The ohmic part of the plasma current (0.6-0.9MA) is very small (Vloop <50mV) for most of the pulses. Different scaling laws were tested with three input parameters: the wave directivity, the plasma current (Ip) or the volume average temperature (<Te>) and the effective charge (Zeff). When applying these scaling laws to four JET pulses, no discrepancy is found except for the high plasma current (Ip = 2.0MA) pulse. Finally the best fit was found by replacing Te (or Ip) by the thermal electron confinement time. This result is supported by the hard X-ray (HXR) diagnostic indicating a fairly good correlation between the plasma edge HXR emission, normalized to the central emission, and the thermal electron confinement time.