Site ranking tends to be "cumulative" and is dependent on the following factors:

• The specific keyword phrases (search terms) that have been targeted
• The overall competitiveness of your industry - how many players are there
• Whether you are targeting a regional, national, or international market
• How well ranking is monitored and the site tweaked over time for SEO improvement
• The progress of your reciprocal linking campaign
• number of competitor sites achieving new ranking themselves