"In previous work based on General Social Survey data, we obtained lead-in factors for the populations of homicides, suicides, and AIDS victims of about 1.60, 1.26, and 1.75, respectively. [Plotz's note: The higher the lead-in, the more likely it is that someone knows more than one victim.] The relatively low figure for suicides points to the relative social isolation and stigmatization of those who commit suicide, while the relatively high figure for AIDS reflects the relatively high social cohesiveness of those afflicted with AIDS despite stigmatization. We think that the figure for homicides reflects the fact that this is a population that is neither stigmatized nor uninteresting and that is generally not a cohesive group (though their survivors might be). We think that people who experienced the attack of September 11 are in this category, so we assume a lead-in factor of 1.60 for these populations."