USA - 3 national polls on the death penalty have been recently published, and each gave different results

3 national polls on the death penalty have been published in recent days, and each gave different results on the main question: would you rather back the death penalty or life imprisonment without parole? For 2 of the surveys the majority of Americans prefer life sentences, for 1 they prefer death sentences. But when in one of the surveys that gives an overwhelming life sentence support, a terrorism hypothesis is added, the results have a dramatic change. On June 1 (see) it was released the Quinnipiac University poll, according to which 48% prefer life imprisonment, and 43% prefer death. On June 4 (see) it was released the Gallup poll, according to which 45% prefer life imprisonment, and 50% death. On June 4 (see) it was also released the ABC News / Washington Post poll, according to which 52% are pro-life imprisonment, and 42% pro-death. The Quinnipiac survey is more accurate because it has a sample of 1,700 respondents, while the other two have 1000. But it is the Quinnipiac poll that may explain such diverse data. Quinnipiac adds two hypotheses: in the case of terrorism, and in the case of Tsarnaev, the young man of Chechen origin that a federal jury on May 15 (see) sentenced to death for the massacre at the Boston Marathon. Assuming generic "terrorism", the percentages becomes life imprisonment 36% against 58% death. Assuming "terrorism" with explicit reference to Tsarnaev, the death percentage rises again, up to 62%, while the “life” option drops to 34%. With these wide variations, an average of the three surveys may be calculated as follows: on the blunt question between life imprisonment and death, on average 48.3% of Americans have responded life imprisonment, 45% death. The inclusion in one of the three surveys of terrorism hypothesis reverses the outcome, and the average is about 51% death and about 44% life imprisonment.