Add percentages for open rate/click-throughs to mailing report

Mailing reports show percentages from some values but not others. I'm curious about this, because it seems like a conscious choice - albeit one made during the Civi 1.x cycle, so it's probably time to review. I suggested to my client requesting this that there are several ways to calculate a "click-through percentage" here, and they gave me a very detailed response (below). I also couldn't figure out why Open Rate didn't have a percentage.

I'll go ahead and submit a PR for this next week. My two questions are:

• Should this be submitted against 4.6.x?
• Does anyone have an objection to this?

From my client:
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Hey folks – I do find the “Click-through summary” section in a CiviMail Report helpful for certain things, like comparing internally how our fundraising emails do (since you can isolate click-throughs to the donation page). But for comparing ourselves with industry standards, or for emails with lots of different click-through options like eNewsletters, you really do need a percentage metric that looks at our members’ engagement with the whole email (not just the link-by-link analysis).

After digging around a bit, CTR is calculated differently by different agencies: SalesForce and most other places it seems measure CTR as the total # of unique clicks divided into the total # of emails delivered, i.e. just removing multiple clicks-throughs from the same individual on a link. M+R’s benchmark reports for the non-profit industry, however, use “the number of people who clicked at least one link in the email divided by the total number of message recipients,” which is a bit different. I’m a bit partial to the M+R metric, since I’d rather know how many of our members are engaged with our emails than to know the “intensity” of engagement, and M+R is also the go-to for non-profit advocacy groups. But perhaps one of these is easier to implement than the other? Here are the sources for the CTR algorithms:

http://www.hfrp.org/evaluation/the-evaluation-exchange/issue-archive/advocacy-and-policy-change/the-enonprofit-benchmarks-study-diving-into-email-metrics

https://www.salesforce.com/blog/2013/07/email-marketing-tips.html

I agree about Open Rates – this one seems like a no brainer!

I’ve shown our Civi setup to two communications professionals so far, and this is the first thing they both complained about!