Trace incentives without assuming people are machines

A parking garage raises its daily price from $8 to $12. One commuter switches to the bus, while another keeps driving because the first bus arrives after their shift starts and no suitable carpool is available. Both responses make sense.

An incentive changes an action's relative benefit or cost. The parking charge makes driving less attractive compared with available alternatives, but predicting the response also requires knowing which alternatives a commuter can actually take. Their constraints matter.

Trace the change through a person's options

A café offers a reusable-cup discount of 40 cents. A customer who already carries a cup can claim it with little effort, while someone buying coffee unexpectedly may have no cup to use. Another forgets the offer.

Effort affects the choice too. Moving a recycling bin beside the ordinary bin reduces the trouble of recycling, while a long registration form adds to the cost of joining a program. Neither change needs a money payment. Attention and uncertainty also affect the decision, particularly when a customer must compare unfamiliar options or work out what an offer requires.

A familiar brand can save a shopper twenty minutes of comparison. That shortcut can be reasonable given the cost of searching, although it may leave the shopper paying for a feature they do not need. Purposeful choice can still be imperfect.

A higher wage can pull in two directions

An extra dollar per hour raises the reward for working, but it also allows someone to earn a given income in fewer hours if they can adjust their schedule. The effects can oppose each other.

The substitution effect encourages work because leisure now costs more in forgone earnings. If leisure is a normal good, the income effect encourages the worker to take additional leisure, with the overall response depending on the two effects' relative strength. Some jobs allow no change in hours.

Name the changed tradeoff before predicting a response. For a worker offered a higher wage, ask how strongly they value extra leisure and whether their employer allows the schedule adjustment you are imagining.

Separate a plausible story from evidence

Suppose reusable-cup use rises after the café introduces its discount. The café might also have added signs or attracted different customers, so a before-and-after comparison cannot by itself isolate the effect of the discount. Several things changed.

A carefully designed comparison can help. Comparable stores could be randomly assigned different offers while other conditions remain similar, with customer mix and implementation checked so the observed difference can be interpreted. Random assignment helps separate the offer from preexisting differences. Spillovers between stores and missing observations still need attention.

When you hear an incentive claim, identify who could respond to the changed reward and ask what evidence separates that response from other changes happening at the same time. For the café, check both the offer and who shopped there.

Watch the idea in action

A related lesson from Marginal Revolution University. Read the examples above alongside the video.

Open the video on YouTube · Educator lesson and source

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