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.