Here is some additional information for those that have requested it.

The data is completely self-reported data. All respondents were given a time line as to when specific events occurred (WTC 1 Hit, Announcement in WTC 2 about WTC 1, WTC 2 Hit, WTC 2 collapsed, WTC 1 Collapsed). Minimally all respondents had some notion as to when thest things happened. They were then asked when (to the best of their ability) to provide the estimated time and floor when they specific actions on their part occurred). Arrived at work?? First became aware that something unusual had happened. Concluded that something serious had happened. Made the decision to evacuate. Began to evacuate (physically). Reached the street access level. Exited on th street. Reached home.

The correlation between where they started and the time between began to evacuate and reached the street is .64.

>>>>>>>I saw the original posting and then watched the exchanges about how to work this problem. I'd like to ask a really basic question, more out of curiosity than anything else. The question is where did these data come from? I read the popularly published account of the attack (the name of which I forget) and find it kind of hard to believe that people could recall very accurately when they started down and when they hit the 'ground floor' however you define that. I doubt also that there were 'official' records of people coming down. To the extent that the accounts in the book are accurate, I'd also think that one's velocity down the stairs depended on when one started down. Velocity would have slowed as volume increased and as rescue people started up. But, mainly, I'm curious of the circumstances of the data's collection.