How to evaluate the reliability of sources

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Reliability is a source evaluation skill which asks you to draw a conclusion about the trustworthiness of a source.


Evaluating historical sources for their reliability is important because it helps us to determine whether the information contained in the source is trustworthy.


Without assessing the reliability of historical sources, we run the risk of accepting false or biased information as true, which can lead to misunderstandings, inaccuracies, and even the propagation of misinformation.

What is 'reliability'?

Reliability of sources evaluates whether they are trustworthy. It is important that the sources you use in your assessment pieces are reliable so that the quotes you use from them can be trusted.


In history, it is rare that we are completely sure that sources are 100% reliable.


Therefore, when we talk about reliability of sources, we can talk in terms of ‘degrees of reliability':


Extremely - Very – Somewhat – Rarely – Not very


For example, we can say that a source is "extremely reliable", or "not very reliable".

Watch a video explanation on the History Skills YouTube channel:

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How do I evaluate reliability?

A judgement of reliability requires three elements:

  1. A clearly stated decision
  2. A 'marker' word to show the link between the decision and the reasons (e.g. because, due to, since, etc.)
  3. Reasons for the decision (from your source analysis)



This source is very reliable because it was written by a professional historian.


As the author was present at the event, his record of it is likely to be very trustworthy.

What reasons can be provided to justify a source's reliability?

Based upon what you discovered in your analysis of the source, the reasons provided to establish reliability can be based upon any of the following:





The creator is someone who can be trusted. For example, an eyewitness or an academic expert.

The type of source is particularly valuable. For example, a personal letter or an academic journal.




The creator has a specific perspective on the topic. For example, a particular nationality or career.




The source was created at an important point in time regarding the event. For example, it was made on the same day.




The intended audience of the source is particularly important. For example, those who would have known key details.




The specific purpose of the source was to record specific information about the topic. 

A paragraph example evaluation of reliability:

Source A is a very reliable source regarding the experience of Australian troops at Gallipoli because it is a letter was written by John Smith, an Australian soldier who was personally involved in the event itself. This source was written a few days after the Gallipoli landing on the 25th of April 1915 and was intended to be a recount of his experiences to be read by his family in Australia. As a result, it is likely to be a very trustworthy account of a soldier’s experience of the Gallipoli landing.

Colour key:
 Origin Perspective Context Audience Motive

What if a source is unreliable?

When using information from sources to prove your own argument, you need to be able to use sources that are reliable.


If you have found a source which you discover to be unreliable, the best advice would be not to use the source.


However, if the source is too relevant to your topic that you cannot use another, use a different evaluation skill to argue for why you are using it, rather than simply arguing that the source is unreliable.

How do I establish unreliability?

Based upon what you discovered in your analysis of the source, you can establish its unreliability based upon any of the following:

  • The creator of the source was not present at the time of the event.

  • The creator of the source does not have a sufficiently educated perspective on the topic. (e.g., they have no formal education in History)
  • The source has not been fact-checked by an educated audience. (e.g., it is a online blog post)

  • The purpose of the source was to be entertaining or to simply give an opinion, rather than focus on the facts, about the topic. 


Demonstrating source reliability in your writing:


This source is mostly reliable regarding factory conditions in the Industrial Revolution because the creator lived next to a major industrial facility during the 19th century.


John Smith, whose own personal experience as a soldier in World War I provides a highly reliable description on the living conditions in the trenches, says “…” (1981, 31).


This official population survey was conducted by the Australian Bureau of Statistics which is responsible for providing the Australian government with official data. As a result, the information provided can be considered very reliable.

Demonstrating source unreliability in your writing:


Plutarch describes what happened, saying, “…”, but he often wrote to entertain so historians can’t always trust what he says (as found in Scott-Kilvert 1960, 76).


The information is drawn from a random website that does not provide information about the author, so it is probably a very unreliable source.

Sophisticated evaluation: values and limitations

As you become more comfortable with evaluating the reliability of sources, you will notice that all sources have limitations, even if they are mostly trustworthy.


To achieve your best marks in evaluating reliability, you need to demonstrate a sophisticated evaluation of historical sources by providing both reasons FOR trusting a source, and also some reasons AGAINST trusting the source.


These are sometimes called the 'values' and 'limitations' of a source.


Please remember, that even though you are providing positives and negatives about the reliability of a source, you still need to come to a judgment about how reliable it is, despite its values and limitations.


Each of the examples below demonstrate sophisticated evaluation of reliability by identifying some values and limitations of sources, while still drawing a clear judgment about its trustworthiness.

Demonstrating a sophisticated evaluation of reliability in your writing:


Plutarch wrote his biography of Julius Caesar over a century after the events he describes, which calls into question the accuracy of the details he provides. However, he drew upon a number of personal documents written by Caesar himself, which increases the trustworthiness of his account. Therefore, despite the concern about the date of its creation, this source is still quite a reliable source about the life of Julius Caesar.


While Miller has a PhD, which seems to indicate that his interpretation can be trusted, it is worth noting that his post-graduate qualifications are in the field of Biology, not in Modern History, which is the topic he was discussing. As a result, Miller is not a very reliable source of information about the rise of Soviet Russia.


Goebbels' personal diary is a valuable record of his beliefs and honest thoughts about the rise of the Nazi party in the 1920s, as he consistently wrote his entries at the end of each day. It must be noted that he was a devoted member of Hitler's inner circle, and due to that fact, his writing only contains the uncritical reproduction of Nazi propaganda from the time. This significantly decreases the likelihood of it being a trustworthy account of what really occurred at the time.

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