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PSSUQ (Post Study System Usability Questionnaire) is a post-task measurement tool which is used to assess system's usability. Current, third version has 16 statements. Each statement has a likert scale from 1 (strongly agree) to 7 (strongly disagree). Each statement also has NA (not applicable) option.

PSSUQ has an overall score which is calculated by averaging the scores given to statements.

User strongly agrees on every statement, PSSUQ overall score is therefore 1.

PSSUQ also has sub-scales for system usefulness (SysUse), information quality (InfoQual) and interface quality (IntQual). Their scores are calculated as:

  • SysUse: averaging scores of statements 1 to 6
  • InfoQual: averaging scores of statements 7 to 12
  • IntQual: averaging scores of statements 13 to 15.

But how should I handle statements that user thinks are not applicable? Do they get the value 0 or do I just ignore them from the calculation? For example in IntQual which has only three statements if NA gets the value 0:

User strongly agrees on two statements and one statement does not apply, IntQual score is 0,667.

If NA is discarded:

User strongly agrees on two statements and one statement does not apply, IntQual score is 1.

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James R. Lewis, who is one the people behind PSSUQ says the following in his paper Psychometric Evaluation of the PSSUQ Using Data from Five Years of Usability Studies:

If a participant chooses not to answer an item, the effect should be to slightly reduce the reliability of the scale in that instance. In most cases, the remaining items should offer a reasonable estimate of the appropriate scale score. From a practical standpoint, averaging the answered items to obtain the scale score enhances the flexibility of use of the questionnaire, because if an item is not appropriate in a specific context and users choose not to answer it, the questionnaire is still useful. Also, users who do not answer every item can stay in the sample.

From this I gather that you should ignore statements that are not applicable and calculate the average of the remaining statements.

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  • Any particular reason why you haven't included the content of the answer as part of your question? I guess you might have thought of it later?
    – Michael Lai
    Nov 9, 2019 at 23:14
  • This is a Q&A website, where you can answer your own questions. Including answer in the question would be against that. Nov 11, 2019 at 13:55
  • We generally try to encourage questions that have shown effort in research in the form of references or attempts at understanding or answering the question so that the community can provide some feedback. Of course, there are occasions when you post a question and then later come across a suitable answer, but by providing an attempted answer in your question it helps to focus on the type of answer that you might be looking for.
    – Michael Lai
    Nov 11, 2019 at 22:44

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