Counting incident responses: incidents.last_resp vs stats.resp_incidents

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Hi,

According to two different out-of the-box reports, I am getting significantly different information about the number of incident responses over a date range.  Why?

The first report is under Service\Incident Reports\Incident Trend\Responses.  It uses incidents.last_resp and reports 268 responses.

The second report is under Service\Incident Reports\Incident Trend\Incident Trend.  It uses stats.resp_incidents and reports that there were 143 responses.

Considering the Responses report is limited to just one response per incident and that, presumably, the Incident Trend would count multiple responses per incident during a range, I would have expected the second report to have the higher number of responses.  Can anyone explain the discrepancy and the relative merits of each report?