Roderick Hindery reported that a number of Western Catholics have voiced significant disagreement with the Church's stance on contraception. Among them, dissident theologian Charles Curran criticized the stance of "Humanae vitae" on artificial birth control. In 1968, the Canadian Conference of Catholic Bishops issued what many interpreted as a dissenting document, the Winnipeg Statement, in which the bishops recognized that a number of Canadian Catholics found it "either extremely difficult or even impossible to make their own all elements of this doctrine" (that of "Humanae vitae"). Additionally, in 1969, they reasserted the Catholic principle of primacy of conscience, a principle that they said should be properly interpreted. They insisted that "a Catholic Christian is not free to form his conscience without consideration of the teaching of the "magisterium", in the particular instance exercised by the Holy Father in an encyclical letter". According to the American Enterprise Institute, 78% of American Catholics say they believe the Church should allow Catholics to use birth control, though other polls reflect different numbers.