After trying various add-on scripts I found that "The best solution is to have all log entries available, and use log analysis tools" as it was mentioned above. I'd recommend the inexpensive but comprehensive and easy-to-interpret tool:
Easy Web Traffic Analysis. Understanding Web Site Visitors and SEO. Web Analytics for Business Owners. Get better ROI!
I use it successfully for the last 1 year. I love auto-reporting feature since I am busy and can forget to download the report for comparison with previous weeks.