he cross-section ratios for the double-to-single ionization of He associated with no projectile charge change (Rq,q), single-electron capture (Rq,q-1) and single-electron loss (Rq,q+1) were measured using coincidence technique. The coincidences resulted from the signals of recoil ions and scattered projectiles. For a given incoming projectile charge state the double-to-single ionization ratios vary strongly with the outgoing reaction channel. It is found that Rq,qRq,q+1Rq,q-1. For direct ionization, Rq,q is nearly independent of the incident projectile charge state. However, for ionization associated with single-electron capture and single-electron loss by the projectile, Rq,q-1 and Rq,q+1 depend strongly on the incident charge state of the projectile. These ionization ratios are interpreted in terms of theories of the atomic polarization effect and the screening and antiscreening effect of the electrons around the core.