The Pew Forum’s survey of international Muslim attitudes asks, among other things,
Some people think that if a woman engages in premarital sex or adultery it is justified for family members to end her life in order to protect the family honor. Do you personally feel that this practice is [often justified, sometimes justified, rarely justified, or never justified].
It also asks the same question about men engaging in premarital sex or adultery.
(1) There’s a vast range of attitudes on the subject in various countries, with “never justified” ranging from just over 80% (in Azerbaijan, Kazakhstan, and Indonesia) to just under 25% (in Afghanistan and Iraq).
(2) In most countries, the respondents’ answers as to “honor killing” of women is very close to their answers as to men, including in many of the countries where there’s a lot of support for such killings. Only a few countries had statistically significant differences, ranging from 47% (81% believe that “honor killing” of men is never justified but only 34% believe that as to women) in Jordan, 10 or 11% in Iraq and Egypt, 7% in Russia, and 14% in the opposite direction in Uzbekistan.
(3) Though the Pew report states, “The Quran and hadith do not condone honor killings, that is, taking the life of a family member who has allegedly brought shame on his or her family,” in a substantial minority of the surveyed countries attitudes towards “honor killings” are significantly correlated to support for imposing Sharia law.
(4) Support for such “honor killings” is shockingly high in some countries. In Afghanistan, for instance, 37% of Muslim respondents say that such killings of women are “often justified,” and 23% say “sometimes justified.” In Iraq, 44% say “often” and 16% say “sometimes.” In Bangladesh, Egypt, Jordan, Lebanon, Pakistan, and the Palestinian Territories, 36% to 41% of respondents say they are often or sometimes justified (and still more say they are justified only rarely).
UPDATE: Commenter SykesFive notes that the question was asked differently in Uzbekistan, Afghanistan, and Iraq (emphasis added): “Some people think that if a woman brings dishonor to her family it is justified for family members to end her life in order to protect the family’s honor….” I don’t know how this might affect the respondents’ understanding of the question, and I assume that the Pew people thought that the italicized clause would be understood as generally referring to supposed sexual misconduct; but it’s certainly worth noting.