Internet users who employ four-word keywords in search engines are more likely to purchase goods or services or receive items of value--such as white papers--than those using one, two, or three words, according to a new report.

For Web-site operators, that means they should create three- and four-word phrases as metadata and keywords to attract visitors.

Oneupweb, a consulting firm specializing in optimizing Web searches, issued a report Tuesday that contends conversion rates peak at four-word keyword phrases or strings, but drop off when longer phrases are used. The one exception: when a single keyword is a corporate name. "People searching for a particular company's name are predisposed to making a purchase or conversion specifically from that company," the 10-page study says.

Researchers define conversion rate as the percentage of unique visitors who purchase or receive items of value or fill out forms at a Web site.

Using aggregate data collected by a proprietary search analytics conversion tool, Oneupweb gathered traffic and conversion data related to search-engine keyword searches during July, October, and December. Oneupweb maintains a database of hundreds of corporate customers including online retailers.

In its analysis of December data, Oneupweb says 38% of users who typed in four words converted their search to an item of value. That compares with 6% for one word; 15%, two; 33%, three; 10%, five; and 9%, six or more.

However, a single keyword representing a corporate name had a 33% conversion rate, while a corporate name coupled with one other keyword dropped the conversion rate to 7%. Findings for July and October were similar to December's results.

Researchers admit they were surprised of the sharp falloff after four words. They suspect searchers using longer strings may be asking specific questions, suggesting they're investigating a product or service and may use a shorter string later when they're ready to take action. Also, search engines might not be effective interpreting five-word searches, returning less relevant results and discouraging conversions.

Oneupweb says companies shouldn't snub single keywords, but they should add relevant multiword keyword strings of up to five words.