September's top online retailer—based on conversion rate—was food home-delivery and mail-order service Schwan's, followed by florist ProFlowers, according to Nielsen.
Download the Excel file of the above data.
Note: Nielsen Online determines conversion rate based on visitors rather than sessions: i.e., No. of unique customers/No. of unique visitors. To qualify for inclusion in the top 10, online retailers had to have a minimum of 500,000 unique visitors during the month.
