How to identify bias in sources

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© History Skills

As you read historical sources, particularly primary sources, you may find yourself noticing that some language used by the source's creator is extreme or obviously one-sided.


When you notice this, you have noticed potential bias. Finding out more about bias helps you draw some powerful evaluations about a source.

What is 'bias'?

Bias is when the creator’s perspective is so strongly for or against something that the information in the source is clearly unbalanced or prejudiced.


All sources contain some degree of bias, but it is not always possible to detect it.


Bias can either be extremely positive or extremely negative.

  • If extremely positive, it is described as “pro-”, or “in favour of”, etc.

  • If extremely negative, it is described as “anti-”, or “strongly against”, etc.

  • If you cannot detect a bias, it is described as a “balanced” source.

Watch a video explanation on the History Skills YouTube channel:

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How do I detect bias in a source?

Look for times in a source where any of the following happen:

  • When describing people or events, the language is too positive and does not admit anything negative
  • When describing people or events, the language is too negative and does not admit anything positive
  • The source fails to mention very important information of which you are aware
  • The source provides clearly incorrect information

If you noticed any of the above in your source, it indicates that the creator has a specific bias about the person or event and wants to communicate in a way that positions the audience to see things from the same perspective.

How do I prove a source is biased?

Once you have discovered bias in your source, prove that it exists. Here is how you do it:

  1. Choose a direct quote from the source the shows a clear demonstration of overly positive or negative language. 
  2. Explain what perspective the creator wanted to convince their audience to have on the person or event based upon this bias.
  3. You may also want to explain what motived the creator to do so.

Please be aware!

However, bias in sources does not automatically make a source unreliable or inaccurate.


Acknowledging which side the source supports simply allows us to highlight gaps in information.


Demonstrating the identification of bias in your writing:


The Gallic Wars has an overt pro-Caesar bias since it portrays him in an obviously positive way, with very little mention of any of his failures.


The Refugee Council of Australia is very biased in favour of refugees since they believe that the Pacific Solution is “illegal” (2007, n.p.).


Andrews has a very one-sided view of the events he describes, which is primarily due to the fact that he is a political activist. This is clear when he describes himself as a victim by saying that his opponents "maliciously assaulted" him (2012, 43). 

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