“participants from collectivist cultures like China and Japan are less likely to spare the young over the old — perhaps, the researchers hypothesized, because of a greater emphasis on respecting the elderly.”
Rolling up the results to a nation may not work because it is possible that the survey is accessible to young people in those specific countries in a higher number than it is for the Asian countries. Bottom line could be that we want to save ourselves and depending on my own age, I may make the selection. And it is also quite natural because a twenty year old person may think that saving someone his/her own age is moral because that person can eventually do something good compared to an old person who doesn’t have a long enough life left. At the same time, a fifty-year old may think that, for any given moment, a fifty-year old person is far more valuable to the society and the nation than a twenty-year old. Hence the demographic of the person making the choice can and possibly do create a bias in the demographic of the final outcome.