Should you buy a paid listing on a search engine site if your Web site already ranks at the top of the results in the actual search listings? This is the year of search engine marketing, and if you’re reading this article, you need to know how to answer this question.

Search engine marketing includes both search engine optimization (also called SEO and Web site optimization) and pay-per-click (PPC) search campaigns.

With SEO, a company works with its site’s architecture to remove any impediments to search engine crawlers, which automatically read and index Web sites. These crawlers look for tags in the site’s HTML code. Marketers can often adjust their tags to improve their "relevance," which is calculated by the search engines using complex algorithms. When the site is determined to be highly relevant to a particular keyword search, it will rank high on the search engine’s results page.

For PPC campaigns, marketers pay for sponsored listings or text-only advertisements at the top of sites such as AskJeeves, Google, MSN, Overture or Yahoo.

More and more companies are asking search engine marketing firms to show them how to use both SEO campaigns and PPC media buys for a profitable strategy. At a minimum, each approach requires that the marketer share a few vital pieces of information: the value of a site visitor, the value of a conversion, the lifetime value of a customer and which site behaviors constitute conversions.

Your search engine marketing firm should be able to help you optimize the mix of paid and free search engine traffic based on metrics. It must also be able to tell you which keywords and phrases to target based on how your audience uses language, as well as how much you should pay for those keywords.

One b-to-b site that sells subscriptions for $175 drove more than 170,000 additional visitors from search engines in a single month through an SEO campaign. The acquisition cost for these additional visitors would have exceeded $40,000 per month with even the most conservative PPC fees. The actual SEO campaign cost less than half of this. Had the company pursued a PPC-only campaign, this content provider could have easily overlooked 2 million yearly search engine visitors—targeted, pre-qualified visitors that convert at a higher level than virtually all other traffic.

Similarly, you can improve the results of your PPC campaigns by insisting that your search engine marketing firm perform rigorous research to distinguish audiences by the way they use language to form queries. This science, called linguistic pattern analysis, yields valuable data on audiences. For example, iProspect’s research department uncovered the following:

• Business owners selling automotive parts search for "auto parts," but consumers search for "car parts." • There are no verbs in health care queries. • Physicians search for "gastro-esophageal reflux disease" and rarely misspell their queries; consumers search for "acid reflux."• Consumers frequently misspell condition and symptom words in health care queries.

So, back to our original question: Should you buy a position in Overture or Google if you already have a top ranking in the actual or free search results of a major search engine? Answer: At the right price, based on your site’s business model and your conversion metrics, you should own as many spots on the search results page as possible. What is the right price? It will vary by Web site and business model, and it will always consider the lifetime value of a customer.

Often we are asked what a campaign’s ROI will be. In return, we ask the prospective client, "What is the value of a visitor?" The room falls silent. We break the silence, "I can tell you what the ‘I’ is (the investment/cost of service), but you need to tell us about the ‘R’ if we’re going to get to ROI."

If neither you nor your vendor understands the linguistic patterns of your audience, it doesn’t matter if you choose SEO or PPC—because neither will work.

Fredrick Marckini

is CEO of iProspect, an Arlington, Mass., search engine marketing firm, and author of the book "Search Engine Positioning." He can be reached at [email protected].