Is the death penalty effective?

Capital punishment, the death penalty, or execution is the sentence of death upon a person by judicial process as a punishment for an offence. Crimes that can result in a death penalty are known as capital crimes or capital offences. The term capital originates from the Latin capitalis, literally "regarding the head". Hence a capital crime was originally one punished by severing the head from the body.
Capital punishment has in the past been practiced in virtually every society, although currently only 58 nations actively practice it, with 95 countries having abolished it (the remainder having not used it for 10 years or allowing it only in exceptional circumstances such as wartime). It is a matter of active controversy in various countries and states, and positions can vary within a single political ideology or cultural region. In the European Union member states, Article 2 of the Charter of Fundamental Rights of the European Union prohibits the use of capital punishment.
As of 2010^[update] Amnesty International considered most countries abolitionist. The UN General Assembly has adopted, in 2007 and 2008, non-binding resolutions calling for a global moratorium on executions, with a view to eventual abolition. Although many nations have abolished capital punishment, over 60% of the world's population live in countries where executions take place, inasmuch as the People's Republic of China, India, the United States of America and Indonesia, the four most populous countries in the world, continue to apply the death penalty (although in India it is used only rarely). Each of these four nations voted against the General Assembly resolutions..
Does that act of sentencing prisoner or convicts to death fair?