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Fig. 1 | BMC Medical Research Methodology

Fig. 1

From: Why item response theory should be used for longitudinal questionnaire data analysis in medical research

Fig. 1

Item response characteristic curves for item 2 from the STAI-DY with four answering categories. The item that was used for this example was ‘I feel nervous and restless’ with four answering categories ‘1. Almost never’, ‘2. Sometimes’, ‘3. Often’, and ‘4. Almost always’. The crossing of two lines mark a threshold and can be interpreted as the location on the latent parameter where the probability of choosing the corresponding category or higher is 0.5

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