In the book You Are Not So Smart, by David McRaney, can you think of intrinsic (personal) and extrinsic (situational) variables that will increase...

There are plenty of intrinsic and extrinsic variables that increase the use of heuristics and biases, as both of these are commonly used by the human brain to simplify and categorize the world. An example of an intrinsic variable that increases reliance on heuristics and biases would be the need for security. Humans have an intrinsic need to feel safe and secure, which leads us to adopt heuristics and biases that keep us safe. While biases can cause us to reject new ideas, people, and experiences because of perceived risk, they also serve the purpose of maintaining security. For example, the ambiguity effect is caused by an intrinsic variable that results in the tendency to avoid making decisions about the unknown. In this case, personal knowledge is the intrinsic variable that leads to the adoption of the ambiguity effect.

An extrinsic variable that leads to the use of heuristics is social confirmation. The bandwagon effect is a bias that refers to the tendency to believe an idea is legitimate simply because many other people have adopted it. This bias relies on extrinsic or situational variables, including the opinions of others and the rate at which an idea or action has been adopted.

Here are four times people use different heuristics:

1) As a consumer

As consumers, we often use the representativeness heuristic to make judgments about the people we see in advertisements. The familiarity heuristic comes into play when we choose brands we recognize over unfamiliar brands. The escalation of commitment heuristic can be seen in the tendency to "stick with" a product or service that worked in the past.

2) As a voter

As a voter, the escalation of commitment heuristic often leads people to remain with the same political party without examining whether it currently serves their beliefs. Naive diversification comes into play when voters are asked to choose from several candidates at once without having a significant amount of information about any of them. Voters tend to choose more diverse options than they would if given a choice of one candidate at a time. The representativeness heuristic also affects how we see political candidates. Based on a small amount of information, such as appearance, we come to a variety of conclusions about a candidate's moral character and prospective performance in office.

3) As a student

As a student, anchoring and adjustment lead to the tendency to rely on information obtained in early classes. Naive diversification makes students guess more broadly than they normally would on tests with multiple answer choices. The escalation of commitment can explain why someone remains in a major that makes him or her unhappy. Because the student has invested time and effort in the major, it is perceived as having more value than the others.

4) As someone’s friend, boyfriend, or girlfriend

The escalation of commitment tends to factor heavily into platonic and romantic relationships. After investing an extensive amount of time and effort into a relationship, people are more likely to try to "make it work" than if they are involved in a new relationship. This heuristic leads people to stay in dysfunctional relationships for much longer than they should. The familiarity heuristic causes people to believe a person's past behavior is an adequate indicator of present behavior, which can lead to conflict and resentment if the partner has gone through significant emotional or behavioral changes. Finally, the anchoring and adjustment heuristic causes people to judge their friends and partners based on their behavior early on in the relationship. This can lead to issues when behavior naturally changes as the relationship progress and each party becomes more comfortable with expressing other facets of his or her personality.