During the summer of 2012, 38% of all mobile check-ins at 10 leading retailers on four social networks occurred at a Wal-Mart Stores Inc. location, according to a new study of data from foursquare, Twitter, Yelp and Instagram by mobile ad network LocalResponse. LocalResponse measured the National Retail Federation top 10 U.S. retailers, counting both explicit check-ins, like those made on social shopping network foursquare when a consumer selects a specific location, and implicit check-ins, such as a Twitter post stating “I’m shopping at Macy’s.” LocalResponse says it could not access check-in data on Facebook because Facebook is a private network.

After Wal-Mart, Target Corp. came in second with 15%, followed by Costco Wholesale Corp. with 9%, Best Buy Co. 7%, Walgreen Co. 6%, The Home Depot Inc. 6%, CVS Caremark Corp. 5%, Lowe’s Cos. Inc. 5%, Safeway 4% and Kroger 4%. The total does not add up to 100% due to rounding.

Saturday is the most popular day of the week for social shoppers: 25.9% of all check-ins registered across the 10 retailers occurred on Saturdays, Local Response finds in its study. This was followed by Friday with 19.7% and Sunday with 14.3%.

Shoppers check in to stores most often between 3 p.m. and 4 p.m. Eastern time on Saturdays, according to the study. This was followed by between 8 p.m. and 9 p.m. Eastern time on Fridays and between 2 p.m. and 3 p.m. Eastern time on Sundays.

54% of check-ins were conducted by men, 46% by women, LocalResponse finds. The largest percentages of male check-ins occurred at Best Buy (67% men) and Lowe’s (65% men), while the largest percentage of female check-ins occurred at Target (53% women). At Wal-Mart, check-ins between the sexes were nearly identical, with men accounting for 51% and women 49%.

78.5% of check-ins in the study were made on foursquare, 17.7% on Twitter, 2.4% on Yelp and 1.4% on Instagram.