We derive the well-known Coulomb correction factor for the Gordon-Volkov wave function describing an outgoing electron in the process of ionization in an intense laser field.Although rigorous treatment would limit its use only to laser fields much lower than the so-called barrier-suppression field,it appears that in practice the correction factor may be used also close to and even above this critical value of the laser field.We compare predictions of several analytical expressions describing ionization rate of the hydrogen atom in its ground state in the strong linearly polarized laser field.We also compare ionization probabilities obtained by integrating these ionization rates over a temporal envelope of the laser pulse with predictions based on the exact numerical solution to the time-dependent Schr?dinger equation.