Several months ago, I wrote a post about some of the ingenious and sometimes sneaky tactics marketers use to get you to make buying decisions. In that piece, I wrote about how stores use every advantage — down to the color of the lights and the temperature of the store — to get you in a “buying mood”.

Recently, there has been some attention paid to an increasingly-common tactic to sway our decision making. Savvy marketers have learned that people are prone to have their decision-making machinery influenced by something called the “decoy effect” (science calls it the “asymmetric dominance effect”). There is a really good post on The Simple Dollar blog.

The decoy effect seems nonsensical on the face of it, but in reality, it has been proven to make otherwise-rational people make irrational decisions or change their decisions altogether. Here’s how it works. Let’s take the example of a car. You are looking for a basic vehicle at a low price, for your daughter going to college. Options are not that important to you; price and safety are your primary considerations.

You go to a dealership and there are two choices, and you’re trying to make a decision. One (Car A) is priced at $17,000, and is a top-rated safety pick. The other (Car B) is priced at $15,000, but is slightly lower on the safety ratings. The salesman, noticing your deliberations, points out that there is a third option (Car C) which is priced at $20,000, but is also top-rated on safety. Now, common sense would dictate that you would not consider car C (why would you; you can get an equally-safe car for less!) But something strange has suddenly occurred in your thinking: you are now bound and determined that Car A is your choice. Sure, you’re paying more than car B, but it’s safer too!

What you didn’t realize is that Car C is a “decoy”, designed to make the Car A more attractive to you. Having a more-costly option on the table influenced you to buy the higher-cost alternative.

The decoy effect is used in a variety of situations, in every level of product marketing, and it’s actually very common in our everyday lives. Various strategies have been suggested for combating it, but I like what the blog The Simple Dollar suggests: unit pricing. For example, when looking at toilet paper, see if you can determine the cost per sheet. I love stores that provide unit pricing; it can often help you decide when something might — or might not — be a better buy for the money. Shopping like this takes time, planning and focus. But it will pay off in the long run.