Table 1 Steps in the Mokken scale analysis for dichotomous items outlined by Stochl et al. [26]

Step 1a

Dimensionality assessment (using the coefH function in the mokken package in R). Produces scalability coefficient for all items (H), item pairs (Hij), and individual items (Hi)). Values for each should be between 0 and 1.

Step 1b

Formation of Mokken scales (using the automated item search procedure or aisp function in the mokken package in R). Items form a coherent scale.

Step 2

Assessment of monotonicity (using the check.monotonicity function in the mokken package in R). Score for an individual item should monotonically increase for an increase in the value associated with the latent trait).

Step 3

Assessment of invariant item ordering (IIO) and non-intersection (using the check.iio function in the mokken package in R). The item characteristic curves for a score of 0 or should not cross as the latent trait changes. IIO is where the ‘difficulty’ of the item does not change as the value associated with the latent trait changes.