When we have scripts that simply navigate to a single page and we run 3 iterations of the webPageTest script for example, the above results analysis works well. We get an average of the test runs aimed at loading this one page.
However, if our script involves going to the home page, logging in and moving on through the site, the data file has rows for each step in the workflow. So the above analysis gives an average across each of those steps. This may still be acceptable, particularly for following trend graphs.
If this is not what you are after there are a few approaches you can take:
1. You can use 'logData 0' and logData 1' in the webPageTest script to determine what is logged and what is not logged, for example you could miss out the home page from the timings.
2. You could adjust the analysis in the JMeter raw processor, potentially even building jtl files for each step in the script. You could still average over those steps as done in the simple case above. The steps can be pulled out of the raw data file based on page title or there is a setEventName option in webPageTest scripts that should come through to this log file in the event name column.
For the moment the solution here is doing what I need it to do so I will leave it to the reader to adjust any of the points raised here for their use. I will post updates to the script if and when I develop any.
Hope this is all of some use to you. If you use it, perhaps an acknowledgment would be good.