## How Individuals Make Choices Based on Their Budget Constraints

Read this section to understand the concept of a budget constraint and how people make decisions when faced with this type of constraint. In economics, a budget constraint is a model that represents two possible things to choose from when spending some income. For example, suppose that you are a store manager and you have $100 to spend on two things for decorations for the store: flower arrangements at$10 each and posters at $5 each. A budget constraint for$100 will then be the different combinations with different number of flower arrangements and posters.

### Identifying Opportunity Cost

In many cases, it is reasonable to refer to the opportunity cost as the price. If your cousin buys a new bicycle for $300, then$300 measures the amount of "other consumption" that he has given up. For practical purposes, there may be no special need to identify the specific alternative product or products that could have been bought with that $300, but sometimes the price as measured in dollars may not accurately capture the true opportunity cost. This problem can loom especially large when costs of time are involved. For example, consider a boss who decides that all employees will attend a two-day retreat to "build team spirit". The out-of-pocket monetary cost of the event may involve hiring an outside consulting firm to run the retreat, as well as room and board for all participants. But an opportunity cost exists as well: during the two days of the retreat, none of the employees are doing any other work. Attending college is another case where the opportunity cost exceeds the monetary cost. The out-of-pocket costs of attending college include tuition, books, room and board, and other expenses. But in addition, during the hours that you are attending class and studying, it is impossible to work at a paying job. Thus, college imposes both an out-of-pocket cost and an opportunity cost of lost earnings. ### Clear It Up #### What is the opportunity cost associated with increased airport security measures? After the terrorist plane hijackings on September 11, 2001, many steps were proposed to improve air travel safety. For example, the federal government could provide armed "sky marshals" who would travel inconspicuously with the rest of the passengers. The cost of having a sky marshal on every flight would be roughly$3 billion per year. Retrofitting all U.S. planes with reinforced cockpit doors to make it harder for terrorists to take over the plane would have a price tag of $450 million. Buying more sophisticated security equipment for airports, like three-dimensional baggage scanners and cameras linked to face recognition software, could cost another$2 billion.

But the single biggest cost of greater airline security does not involve spending money. It is the opportunity cost of additional waiting time at the airport. According to the United States Department of Transportation (DOT), more than 800 million passengers took plane trips in the United States in 2012. Since the 9/11 hijackings, security screening has become more intensive, and consequently, the procedure takes longer than in the past. Say that, on average, each air passenger spends an extra 30 minutes in the airport per trip. Economists commonly place a value on time to convert an opportunity cost in time into a monetary figure. Because many air travelers are relatively high-paid business people, conservative estimates set the average price of time for air travelers at $20 per hour. By these back-of-the-envelope calculations, the opportunity cost of delays in airports could be as much as 800 million × 0.5 hours ×$20/hour, or $8 billion per year. Clearly, the opportunity costs of waiting time can be just as important as costs that involve direct spending. In some cases, realizing the opportunity cost can alter behavior. Imagine, for example, that you spend$8 on lunch every day at work. You may know perfectly well that bringing a lunch from home would cost only $3 a day, so the opportunity cost of buying lunch at the restaurant is$5 each day (that is, the $8 buying lunch costs minus the$3 your lunch from home would cost). $5 each day does not seem to be that much. However, if you project what that adds up to in a year ­– 250 days a year ×$5 per day equals $1,250, the cost, perhaps, of a decent vacation. If the opportunity cost is described as "a nice vacation" instead of "$5 a day," you might make different choices.