How are average "Rates" calculated?

[Nate_Oosterhous]

I am wondering how average rates calculated with email marketing metrics.  I may be just driving myself insane but wanted to clarify.

Example:

Let's say you sent 3 emails out all time and below are the metrics for each send.

                   Delivered        Opens       % Opened

Email 1:         1000             150                  15%

Email 2:         2300             430                 18.7%

Email 3:         400               180                   45%

Is your average open rate 20.54% (Calculated by SUM OF EMAILS OPENED/SUM OF EMAILS DELIVERED)?

OR

Is you average open rate 26.23% (Calculated by (15% + 18.7% + 45%)/3) ?

[SanfordWhiteman]

Depends on what you want to express, plus how comprehensible it'll be to the person looking at it, who typically is non-technical (but may think they are!). Always the catch with any reports, right?

The former isn't an average, it's just a ratio. But that doesn't mean it's irrelevant.

The latter is how you would calculate "average open rate per campaign". Of course you can also see how using the mean for 3 events is pretty skewy.

[Nate_Oosterhous]

I agree Sanford.  Do you know what all the different benchmark reports out there use for when they talk about average open rates?

Since I don't have a clear understanding of what "Open Rate" really refers to....some say it is a ratio....some say it is an average....I don't know what to compare to industry "average open rates".

Basically am looking to identify what metric are we exactly supposed to compare against "industry average open rates" from benchmark reports.  How is that metric calculated?