Experimental observations and turbulence simulations have clearly identified the essential roles of local ExB shear, safety factor and magnetic shear, for triggering ITBs. Therefore, the amount of power required for ITB formation, so-called power threshold Pth depending on local plasma parameters, varies among different devices and additional heating methods. Previous analyses of the international ITB database [1, 2, 3], which has been compiled from experimental results of 9 tokamaks (AUG, DIII-D, FTU, JET, JT60, RTP, T10, TFTR, Tore Supra), have shown that the power threshold is a complex function of global parameters (Ip, B, a, n,...). The main finding of this work is that the variation of Pth is strongly correlated with the normalized Larmor radius r* (r* = riq/a). Pth is found to be reduced by a factor of more than 2 for r* 5.10-3. This feature is consistent with ITG theory and recent gyrokinetic simulations [4], which predict a transition from Bohm to gyro-Bohm when r* decreases. A favourable effect of negative/weak magnetic shear in reducing Pth is also reported. Finally, transport (with CRONOS code) and stability (with KINEZERO code) studies of a series of JET discharges with a systematic scan of r* are presented together with the global analysis.