Fig. 3

The test information curves of the Itm package in R (v4.0.2; R Core Team 2021) under the Graded Response Model (GRM). (Note. Latent trait θ is shown on the horizontal axis, the θ range from − 0.9 to 3.5, and the amount of information and standard error generated by testing at any trait level is shown on the vertical axis. The peak of the curve corresponds to a high reliability value at a theta value of -0.9, suggesting that C-GPS is reliable for mild to very severe chronic pain)