Why sleep on a purchase

Have you ever bought something on the way home after an exhausting day, then looked at it the next morning and wondered why? Researchers have names for two tendencies that seem to be involved in purchases like that.

What we know

1. The pull of the present (present bias)

Stephan Meier and Charles Sprenger asked lower-income people in the US to choose between a smaller amount now and a larger amount later. They then matched each person’s choices with their credit records.

People who strongly preferred “now”, that is, those with present bias, carried substantially more revolving credit card debt. The link held even after accounting for differences in income and in how much people were able to borrow.

2. A tired mind and impulse buying

Kathleen Vohs and Ronald Faber ran experiments in the US. Some participants first did a task that used self-control, such as suppressing their thoughts. Compared with others, those who had just used self-control felt a stronger urge to buy and actually spent more money.

How to read it

The two studies differ in strength.

• The present bias study is correlational. It does not show that present bias caused the debt. It also comes from lower-income people in the US.
• The impulse buying study is experimental, but needs care. It rests on the idea that self-control is a resource that runs down with use, known as ego depletion. Replication efforts since then have often failed to find the same effect, so that theory is now in doubt. In one preregistered replication run the same way in 23 labs with 2,141 participants, the effect was close to zero (X-hagger-2016). A fair reading is “being tired may make impulse buying more likely”.
• We found no randomized trial that directly tested whether waiting a night reduces wasteful spending. We also found no study from Japan.

Even so, waiting a night rests on a sensible idea. Present bias is a strong pull toward right now, so moving the decision a little later takes you out of that pull. Not deciding while tired points the same way. It costs almost nothing in time or money, and it is hard to lose by it.

Why include a study whose theory is in doubt? Because leaving it out would make the case look tidier than it is. The honest summary is that the reasoning for waiting a night is sound, while the direct evidence is still thin.

A small step today

Try the app habit “Waited a night before buying” like this:

• For any unplanned purchase, stop at putting it in the cart or writing it down. Decide the next morning.
• Make late-night or tired online shopping “browse only”.
• If you still want it after a night, go ahead and buy it. The point is not to deny yourself. It is to decide with tomorrow’s self instead of tonight’s mood.
• The next morning, whether you bought it or not, also log “Tracked spending”. Over time you will see when the urge to buy tends to hit you.

On the days you wait, log it in the app.

Sources

• [D10] Meier & Sprenger (2010) Present-Biased Preferences and Credit Card Borrowing. American Economic Journal: Applied Economics.
• [D11] Vohs & Faber (2007) Spent Resources: Self-Regulatory Resource Availability Affects Impulse Buying. Journal of Consumer Research.
• [X-hagger-2016] Hagger, Chatzisarantis et al. (2016) A Multilab Preregistered Replication of the Ego-Depletion Effect. Perspectives on Psychological Science.