I found this one through Hendry Lee's blog:
Journal of Interactive Advertising has published an academic paper studying email and postal direct marketing. Here are the hypotheses drawn from this study:
- Consumers are likely to find spam more intrusive than direct mail.
- Ad intrusiveness caused by a) spam; b) postal direct mail negatively correlates with attitudes toward the advertising technique.
- The level of perceived loss of control by consumers will be greater for spam than direct mail.
- Perceived loss of control mediates the relationship between ad intrusiveness caused by spam and ad irritation.
- Consumers are likely to experience a higher level of advertising irritation from spam than direct mail communications.
- The degree of advertising irritation caused by a) spam; b) postal direct mail is negatively correlated with attitudes toward the advertising technique.
For methods of measurements, refer to the paper for details.

Tamara Gielen is an independent email and digital direct marketing
consultant with over 10 years of experience in online, email and direct marketing.