What the professor has determined with a complex computer algorithm for consumer electronics, others have found through less scientifically rigorous means for other products, including clothing and toys: despite all the ads that suggest otherwise, the lowest prices tend to come at other times of the year.

In the case of toys, stores actually offer the steepest discounts in the weeks immediately following Thanksgiving because they want to unload the inventory not swept up on Black Friday, said Dan de Grandpre, who has tracked deals for 15 years at Dealnews.com.

“Toys have a very short shelf life,” he said.

“On Dec. 26, they’re not really useful to retailers anymore, so they have to get rid of it and start slashing prices early in December.”

And it is a precise window of opportunity. In the week or so before Christmas, toy prices shoot back up, Mr. de Grandpre’s tracking shows, as last-minute shoppers come stampeding for Barbies and Lego sets and stores are less desperate “because they’ve been able to reduce their inventory.”