Clinical effectiveness is the extent to which specific clinical interventions do what they are intended to do, i.e maintain and improve the health of patients securing the greatest possible health gain from the available resources
NHS Quality Improvement Scotland (NHS QIS 2005)
It is described as the right person (you) doing:
Clinical effectiveness is thinking critically about what you do, questioning whether it is having the desired result, making a change to practice. It is based on evidence of what is effective in order to improve patient care and experience. This can happen at NHS Board, directorate, department or team, or individual level.