Scientific objectivity

Scientific objectivity is an ideal goal that scientists strive to achieve. Unfortunately, because science is a human enterprise, complete objectivity can never be attained. However, the scientific method is designed to safeguard against bias as much as is possible.

Truth to nature and the origins of scientific objectivity
The modern concept of scientific objectivity didn't come into existence until the 19th century. The concept of "truth to nature," employed in early scientific atlases, was the forerunner of scientific objectivity. The idea behind truth to nature was to present an idealized version of the object under investigation, which was often done using composite drawings. A large interpretive (i.e., subjective) element was thus inherent in this process. During the mid-19th century, realistic depictions came to be valued over idealized ones and objectivity came to be seen as a moral virtue, giving a new meaning to truth to nature. Individual objects were depicted in atlases instead of composite drawings. The invention of photography during this period allowed for easier standardization of pictures in the atlases. Interpretation and value judgments were de-emphasized as the modern concept of scientific objectivity emerged.

Sources of bias

 * Experimenter bias. Everyone (yes, even those scientific paragons of rationality) is subject to cognitive biases.
 * Publication bias. The "publish or perish" system has been implicated in biasing research toward positive results.
 * Politicization of science. He who holds the purse strings and all that. Eugenics and Lysenkoism are notorious examples.
 * Fraud. Pretty simple. Don't have the data? Fabricate it!

Methods of limiting bias
There are a number of methods used to limit bias in the course of carrying out an experiment or scientific investigation. What these methods are will vary by discipline, but there are some common ways this is accomplished.
 * Choosing a falsifiable hypothesis.
 * The use of a control group.
 * The use of double-blinding and randomization, especially in medical trials.
 * Submitting research to peer review.
 * Making data available.
 * Replicating previous results.

Challenges to the concept of objective and value-free science

 * Thomas Kuhn's concept of paradigm shifts.
 * Marxist critiques of "capitalist science," especially by the radical science movement of the 1960s-70s.
 * Helen Longino's argument that values will tend to affect the choice of a theory when it is underdetermined by data.
 * The degree to which perception and observation is theory-laden as demonstrated by cognitive science.
 * Postmodernism