Bias is an inclination of temperament or outlook to present or hold a partial perspective at the expense of (possibly equally valid) alternatives in reference to objects, people, or groups. Anything biased generally is one-sided and therefore lacks a neutral point of view. Bias can come in many forms and is often considered to be synonymous with prejudice or bigotry.
In statistics 
In statistics, there are several types of bias: Selection bias, where there is an error in choosing the individuals or groups to take part in a scientific study. It includes sampling bias, in which some members of the population are more likely to be included than others. Spectrum bias consists of evaluating the ability of a diagnostic test in a biased group of patients, which leads to an overestimate of the sensitivity and specificity of the test. The bias of an estimator is the difference between an estimator's expectation and the true value of the parameter being estimated. Omitted-variable bias is the bias that appears in estimates of parameters in a regression analysis when the assumed specification is incorrect, in that it omits an independent variable that should be in the model. In statistical hypothesis testing, a test is said to be unbiased when the probability of rejecting the null hypothesis exceeds the significance level when the alternative is true and is less than or equal to the significance level when the null hypothesis is true. Systematic bias or systemic bias are external influences that may affect the accuracy of statistical measurements. Data-snooping bias comes from the misuse of data mining techniques.
In judgment and decision making 
A cognitive bias is the human tendency to make systematic decisions in certain circumstances based on cognitive factors rather than evidence. Bias arises from various processes that are sometimes difficult to distinguish. These processes include information-processing shortcuts, motivational factors, and social influence. Such biases can result from information-processing shortcuts called heuristics. They include errors in judgment, social attribution, and memory. Cognitive biases are a common outcome of human thought, and often drastically skew the reliability of anecdotal and legal evidence. It is a phenomenon studied in cognitive science and social psychology. A cognitive bias also has the tendency to make systematic decisions in certain situations.
In the media 
Media bias is the bias of journalists and news producers within the mass media, in the selection of which events and stories are reported and how they are covered. The term "media bias" implies a pervasive or widespread bias contravening the standards of journalism, rather than the perspective of an individual journalist or article. The direction and degree of media bias in various countries is widely disputed.
Practical limitations to media neutrality include the inability of journalists to report all available stories and facts, and the requirement that selected facts be linked into a coherent narrative (Newton 1989). Since it is impossible to report everything, selectivity is inevitable. Government influence, including overt and covert censorship, biases the media in some countries. Market forces that result in a biased presentation include the ownership of the news source, concentration of media ownership, the selection of staff, the preferences of an intended audience, and pressure from advertisers.
Political bias has been a feature of the mass media since its birth with the invention of the printing press. The expense of early printing equipment restricted media production to a limited number of people. Historians have found that publishers often served the interests of powerful social groups.
Other aspects 
- Economic: when people/government interpret a law/contract in their favor for economic reasons.
- Inductive bias in machine learning.
- Cultural bias: Interpreting and judging phenomena in terms particular to one's own culture.
- Racism, regionalism and tribalism: Judging people or phenomena associated with people based on the race/ethnicity, region of origin, or tribe of the people, rather than based on more objective criteria.
- Sexism: Judging based on gender, rather than on more objective criteria.
- Sensationalism: Favouring the exceptional over the ordinary. However this sentence structure makes is sound like an appeal to popularity or normalcy fallacy. This is actually a more complex problem, whereby, the proponent elevates the importance of the evidence to more subjects than it is relevant. This is accomplished by willful bias, assumption or, putting conclusion ahead of evidence. In practice, this includes emphasizing, distorting, or fabricating exceptional news stories to boost popularity.
- Funding bias in scientific studies also known as the agent-principle dilemma.
- Medical bias is also known as a physician having a conflict of interest.
See also 
- Detection theory
- Experimenter's bias
- Reporting bias
- Publication bias
- List of biases in judgment and decision making
- Scholarly method
- Social desirability bias
- Source criticism
- Weasel word
- Wilcox, C. W. (2011) Bias: The Unconscious Deceiver. Bloomington, IN: Xlibris Corporation.
- Ann Heinrichs, The Printing Press (Inventions That Shaped the World), p. 53, Franklin Watts, 2005, ISBN 0-531-16722-4 [Amazon-US | Amazon-UK], ISBN 978-0-531-16722-9 [Amazon-US | Amazon-UK]
- Cain, D.M. and Detsky, A.S. Everyone's a Little Bit Biased (Even Physicians) JAMA 2008;299(24):2893-289.