21st Century Sales

Goodness, if only there were a formula that we could apply that would answer this question!
I've been trying to track down statistics on this for some time. When doing research on the Internet, I keep running across the following:

According to the National Sales Executive Association

• 2% of sales are made on the 1st contact
• 3% of sales are made on the 2nd contact
• 5% of sales are made on the 3rd contact
• 10% of sales are made on the 4th contact
• 80% of sales are made on the 5th-12th contact

Assuming a "contact" could be a face to face meeting, a telephone call, an email, a voice mail message, a fax, a letter (remember those?) or a message with the gatekeeper, it makes sense as most of th time, we need time and a few gentle nudges to part with our hard-earned cash.

I could take this post in all sorts of directions, but first, I want to challenge the data. While these stats are all over the Internet (try searching for "National Sales Executive Association" and you will see), there is no National Sales Executive Association!

Next stop is the business section of the public library, but in the meantime, I'd be grateful to anyone who could point me in the direction of the source of these or similar statistics.