Each click on a paid search ad in April cost 3% less than it did a year ago, yet the return on those clicks continued to increase, according to the new Rewind Index from search engine marketing provider PM Digital. Click costs also were down 3% in March and 2% in February compared with the corresponding months a year ago.

Consumers who clicked through a paid search ad generated 33% more sales for e-retailers during April compared with a year ago. The index measures paid search performance monthly and is based on data from more than 50 large retailers that are clients of PM Digital.

The number of paid search ads clicked on by consumers during the month increased 18%, which led to e-retailers spending 13% more on search ads compared with the same month last year. The conversion rate from paid search ads was up 11% during April and average order value increased 3%.

The index does not include actual dollar amounts.

During April, the top days for retailer sales coming from paid search clicks were April 15 and April 16, a Sunday and Monday. PM Digital suggests consumers may have been drawn to shop by numerous sales promotions tied to the federal income tax filing deadline. PM Digital’s analysis also suggests Sundays are becoming a bigger day for online shopping. With the exception of Easter Sunday, in April, Sundays produced strong sales from paid search, PM Digital says.

Craig Handelsman, chief information officer at e-retailer CentralVacuumStores.com, will explain how he improved his paid search campaigns to attendees at the Internet Retailer Conference & Exhibition 2012 in Chicago in June during a session titled “Shifting a paid search campaign into overdrive with new Google tools