Search engines find and catalog web pages through spidering (also known as webcrawling) software. Spidering software "crawls" through the internet and grabs information from websites which is used to build search engine indexes. Unfortunately, not all search engine spidering software works the same way, so what gives a page a high ranking on one search engine may not necessarily give it a high ranking on another. Note that rather than waiting for a search engine to discover a newly created page, web designers can submit the page directly to search engines for cataloging.
As I had a teacher at school who was always really picky on how to draw conclusions I must say that the conclusions you drew for your health situation might be true, but dangerous. For example: If slightly more women than men suffer from health deseases it could be wise to write the information toward women. But, if you take search behaviour into account thing could look a lot different: It might turn up that men search more than women or that (senior) men are more present on the net than women.
What is Search Engine Optimization (also known as SEO)? A broad definition is that search engine optimization is the art and science of making web pages attractive to search engines. More narrowly, SEO seeks to tweak particular factors known to affect search engine standing to make certain pages more attractive to search engines than other web pages that are vying for the same keywords or keyword phrases.
An SEO technique is considered white hat if it conforms to the search engines' guidelines and involves no deception. As the search engine guidelines are not written as a series of rules or commandments, this is an important distinction to note. White hat SEO is not just about following guidelines but is about ensuring that the content a search engine indexes and subsequently ranks is the same content a user will see. White hat advice is generally summed up as creating content for users, not for search engines, and then making that content easily accessible to the online "spider" algorithms, rather than attempting to trick the algorithm from its intended purpose. White hat SEO is in many ways similar to web development that promotes accessibility, although the two are not identical.
Early versions of search algorithms relied on webmaster-provided information such as the keyword meta tag or index files in engines like ALIWEB. Meta tags provide a guide to each page's content. Using metadata to index pages was found to be less than reliable, however, because the webmaster's choice of keywords in the meta tag could potentially be an inaccurate representation of the site's actual content. Inaccurate, incomplete, and inconsistent data in meta tags could and did cause pages to rank for irrelevant searches.[dubious – discuss] Web content providers also manipulated some attributes within the HTML source of a page in an attempt to rank well in search engines. By 1997, search engine designers recognized that webmasters were making efforts to rank well in their search engine, and that some webmasters were even manipulating their rankings in search results by stuffing pages with excessive or irrelevant keywords. Early search engines, such as Altavista and Infoseek, adjusted their algorithms to prevent webmasters from manipulating rankings.
I completely agree that defintion of a target audience isa great first step, but would ask if adding in competitors to the analysis (mentioned here as a later step) helps draw out who your target audience would be via comparisons, i.e. showing who you are an who you are not - would be very interested to hear opinions on how this tactic can be used within the overall step in coordination with targeted keyword discovery.