It is correct that only timeintervals where an event happens is included in the analysis. That should be understood in the way, that if some person have an event at some time, then other persons interval at that time do matter, because they were at-risk at that time. The programming steps are applied to all records where an event-times occur. That means, the programming steps are applied multiple times to each record, and a number of times proportional to N^2, (or rather N x number-of-events). Event-times are where events occurs. Intervals-endpoints can be either censored or non-censored (equivalent to non-event and event). Typically, all intervals except the last one will be non-events (censored). About the weighted average, I agree on your statement. I wrote it wrong, you did it right!
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