Calculating Email opening rates is Reliable Indicator of Subscribers response?
Email Opening Rates - Track them to follow Email marketing response.
DON'T RELY ON EMAIL OPENINGS ALONE TO CALCULATE YOUR EMAIL MARKETING PROFITS.
Also keep in mind that there might be some disparity in the email opening rates and click tracking rates.
Why?
As I said in this article not all email clients allow image display by default. So the pixel image tracking in HTML emails is not quite reliable.
See the images below from Hotmail email client:

Hotmail blocks the images by default. Unless your subscriber(s) have enabled image display these email openings are not being tracked. To display the images in Hotmail, your subscribers have to click on 'Mark as Safe' link. But what percentage of subscribers actually click the link?
Another image from Squirrelmail email client:

Though the html option is enabled, still the images are not displaying unless the subscribers clicks on 'View Unsafe images' link.
So perfect tracking of the email openings is a hard nut to crack ...