What do sources mean when they say ‘I don’t know’?

A series of posters by CREST Researcher Lorraine Hope illustrate examples of what sources might mean when they say, ‘I don’t know’ or ‘I don’t remember’.

During an interview a source may respond to a question with either ‘I don’t know’ or ‘I don’t remember’. This may well be a legitimate response. However, these responses may also reflect several cognitive, social and motivational states. Therefore, there are many reasons why they might respond with an ‘I don’t know or ‘I don’t remember’.

There are many reasons why a source might respond with an ‘I don’t know or ‘I don’t remember’

Drawing on published research from a variety of sources, Professor Lorraine Hope has developed a taxonomy of the potential reasons for these responses, to help interviewers explore, understand and potentially respond in ways that help elicit further information.

I Don't Know Posters IMAGE – AllThrough a series of posters, Professor Hope provides examples that illustrate each reason along with possible responses. These six posters can be downloaded and shared under our Creative Commons licence:

  • Overview – a summary of the many reasons why a source would say ‘I don’t Know’ or ‘I don’t remember’.
  • Memory Encoding – reasons that relate to factors at memory encoding, such as attention, distraction, reduced psychological capacity.
  • Memory Retrieval – reasons relating to memory retrieval, such as forgetting, uncertainty and metacognition, lack of retrieval support.
  • Interview Context – reasons relating to interview context, such as pragmatic communication, impression management and inferences about the interview.
  • Distrust, Cynicism and Hostility – reasons that relate to distrust, cynicism and hostility such as trust and control issues, perceptions of efficacy and deliberate deceit to mislead.
  • Personal Motivation – reasons that relates to motivational factors such as reluctance (fear, protecting others), status insecurity and ideological motivations e.g., taboo, shame, identity as an ‘informer’.

You can see all the posters here.


Lorraine Hope is a CREST Researcher and Professor of Applied Cognitive Psychology at the University of Portsmouth.

These posters are produced under a Creative Commons 4.0 BY-NC-SA licence. This means you are allowed to use them, with attribution, but we’d also love to know where and how you are using them so please let us know by emailing us at info@crestresearch.ac.uk.

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