Implicit bias is defined as the attitudes or stereotypes that affect our understanding, actions, and decisions in an unconscious manner. Because implicit bias is unconscious, it falls outside our ability to meaningfully introspect about it, meaning that psychologists who seek to understand implicit bias cannot simply ask subjects why they are implicitly biased. Instead, social scientists have taken up a number of other ways to understand its causes and manifestations.
Almost everybody displays implicit bias in one way or another. The most recent large-scale data set to confirm the systemic nature of implicit bias was conducted by a team of researchers at Harvard in 2010. In a review of more than 2.5 million Implicit Association Tests, they found that implicit preferences and stereotypes were "widespread across gender, ethnicity, age, political orientation, and region."
Everyone harbors bias, but not everyone harbors it in the same way. Men showed stronger bias than women. Whites and Asians have stronger social group preferences than other races. Adults over 60 and conservatives had stronger bias in favor of higher-status groups than other groups of people. White respondents had an implicit preference for white people and bias against black people; black people, on the other hand, showed an implicit bias against white people but no concomitant preference toward people of their own race.
These results are presented here in somewhat simplified form to make the point that while implicit bias is pervasive and non-homogenous. It takes many forms, depending on both the characteristics of the respondent and the relative social hierarchy of the subject categories in the test.
One of the most common responses to evidence of widespread implicit bias is denial. "Certainly these tests wouldn't show any problem with me!" I encourage you to resist this natural response. Possessing implicit bias is not tantamount to being racist or sexist, and noting that an individual in a group has implicit bias is not equivalent to calling someone racist or sexist. Instead, we are exploring a well-document psychological phenomenon that, if ignored or left to fester, will perpetuate existing racial and gender disparities. It is much less racist to acknowledge and combat unconscious manifestations of bias than to ignore them.