While individual campaign reporting is valuable, comparing campaigns over time can give you great insight into your email newsletter performance.
To see how campaigns are trending, use the compare tool on your "Sent Campaigns" page, as shown here:
The Compare button appears when you click select all in the toolbar below your campaigns, or when you tick more than one checkbox in the "compare" column.
You can compare up to 100 sent campaigns, but you'll likely get the most value by being more selective and comparing a smaller set. This is particularly helpful if you've made some changes to your campaign copy, design, or list gathering, and want to see if it has made a difference.
Here's an example of a comparison report page:
Use the Export button at the bottom of this page to download your comparision report as a CSV file, or tab delimited text file.