Hidden biases is not only one of the book’s key terms, it’s also one of the main themes. The book centers on the idea that most people hold prejudices of which they are unaware. While a “small minority” (209) of individuals are “overtly prejudice” (209), according to the authors, many others hold implicit biases. The authors demonstrate that these biases can be revealed through a psychology test known as the Implicit Association Test (IAT), which was developed in the 1990s by Anthony G. Greenwald—who is also one of the authors. Greenwald went on to develop the Race IAT, which measures racial bias, but other subsequent IATs have been devised to examine biases for gender, age, and other social categories.

The authors understand hidden biases as a type of “blindspot” or “mindbug”—an error in judgment based on one’s “ingrained habits of thought” (4). They place hidden biases at the heart of most discriminatory behavior in society—arguing that discrimination in general is primarily inadvertent. In other words, people do not intend to be prejudiced. They do not engage in “overtly racial hostile actions” (52) but are instead plagued by implicit negative judgments that directly affect their behavior. The authors consider the act of stereotyping as a type of hidden bias.