If you had to guess the percentage of Americans who dwell on the dark side of the digital divide, what would it be? 5%? 10%? What about 20%?

Answer: 20% of U.S. adults, for a number of reasons, have little use for the Internet.

The Pew Internet Research Project calls it a “digital desert” that’s populated by senior citizens, low-income families and households where Spanish is primarily spoken.

The lesson here: Businesses and organizations relying on Internet-only formats might be missing a sizable chunk of their target audience.

Those same marketing campaigns are likely to leave out many adults with disabilities or illnesses, because a significant slice of that audience — 27% — doesn’t see the Internet as a lifeline.

What’s more, nearly half — 43% — of adults who didn’t graduate from high school use the Internet, compared with 71% of high school grads and 94% of college grads.

A rundown of some of the reasons cited for not using the Internet:

• Don’t have a computer — 12%
• Too expensive — 10%
• It’s too difficult — 9%
• It’s a waste of time — 7%

It doesn’t mean that these audiences, just because they don’t rely on the Internet, will miss out on your message. It’s a reminder to keep more conventional means of contact in mind — radio, mail, TV — if you’re trying to reach the biggest swath of the marketplace.

Tags: Internet, Pew, research