Google's order of results are "automatically determined by more than 100 factors, including our PageRank algorithm, according to the Google Webmaster Info. Google updates its index about once a month and in each update of its database of web pages, the index invariably shifts: Google finds new sites, lose some sites, and sites ranking may change.

 

Google says: Your rank naturally will be affected by changes in the ranking of other sites.

 

Google's order of results is automatically determined by several factors, including our PageRank algorithm. To know more, read Google's Technology Overview.

 

IMPORTANT! Google says: You may want to check and see if the number of other sites linking to your URL has changed. This is the single biggest factor in determining what sites are indexed by Google, as we find most pages when our robots crawl the web and jump from page to page via hyperlinks. To find out who links to your site, use Google's link: tool.