method because the monitor reading is objective and is not affected by sleep quality as BBT can be. Calendar-based Calendar-based methods determine fertility based on a record of the length of previous menstrual cycles. They include the Rhythm Method and the Standard Days Method. The Standard Days method was developed and proven by the researchers at the Institute for Reproductive Health of Georgetown University. CycleBeads, unaffiliated with religious teachings, is a visual tool based on the Standard Days method. According to the Institute of Reproductive Health, when used as birth control, CB has a 95% effectiveness rating. Computer programs are available to help track fertility on a calendar. Lactational amenorrhea The lactational amenorrhea method (LAM) is a method of avoiding pregnancy based on the natural postpartum infertility that occurs when a woman is amenorrheic and fully breastfeeding. The rules of the method help a woman identify and possibly lengthen her infertile period. Debates Roderick Hindery reported that a number of Western Catholics have voiced significant disagreement with the Church's stance on contraception. 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." Catholics for a Free Choice claimed in 1998 that 96% of U.S. Catholic women had used contraceptives at some point in their lives and that 72% of U.S. Catholics believed that one could be a good Catholic without obeying the Church's teaching on birth control. According to a nationwide poll of 2,242 U.S. adults surveyed online in September 2005 by Harris Interactive (they stated that the magnitude of errors cannot be estimated due to sampling errors, non-response, etc.), 90% of U.S. Catholics supported the use of birth control/contraceptives. A survey conducted in 2015 by the Pew Research Center among 5,122 U.S. adults (including 1,016 self-identified Catholics) stated 76% of U.S. Catholics thought that the Church should allow Catholics to use birth control.