Returns aggregate results for a survey plus the individual responses behind them: totals for completed, abandoned, timed-out and error responses, a completion rate as a percentage, and per-question analytics. Optional metrics include average and median completion time in seconds, daily trends, a drop-off funnel, an hourly distribution, unique and repeat callers, and results grouped by referrer. A caller who hung up counts as abandoned, and per-question and referrer ratings are calculated from completed responses only. Date bounds cover whole days: start_date from 00:00:00 and end_date through 23:59:59.