It’s in the search engine; best interests to keep their method a secret; after all, if they publish a list of dos and don’ts and just what what their limits and boundaries are then the spammers, would know the limits of the search engines’ spam catching techniques.
Also secrecy leaves the search engines free to modify things any time they need to. Google changes their algorithm frequently. For instance in just six months in 2007, Google’s algorithm changed 450 times.
No one knows what changes, how big the changes were, or when exactly they occurred. Instead of giving out the algorithm, search engines merely provide guidelines as to their preferences.
This is why that SEO is an art, not just a science: Too many unknown factors are out of your control, so a lot of finesses and intuition is involved.
Other factors can complicate rankings as well. Here’s a brief list of factors that have nothing to do with changes in the web sites themselves that can cause search engine rankings to fluctuates:
• The search engine changed its algorithm and now weighs factors differently.
• The search engine may be testing something new (a temporary change).
• The index being queried is coming from a different data center. Google for instance, has more than 100 data centers in different locations, which may have different versions of the index.
• The search engine had a technical problem and restored data temporarily form cache or a backup version.
• Data may not be up-to-date (depending on when the search engine last crawled the web sites).
Search Engine Secrecy
