What are the minimal sample size requirements for Mokken scaling? An empirical example with the Warwick- Edinburgh Mental Well-Being Scale.

Sample size in Mokken scales is mostly studied on simulated data, reflected in the lack of consideration of sample size in most Mokken scaling studies. Recently, [Straat, J. H., van der Ark, L. A., & Sijtsma, K. (2014). Minimum sample size requirements for Mokken scale analysis. , , 809-822] provided minimum sample size requirements for Mokken scale analysis based on simulation. Our study uses real data from the Warwick-Edinburgh Mental Well-Being Scale ( = 8463) to assess whether these hold. We use per element accuracy to evaluate the impact of sample size, with scaling coefficients and confidence intervals around scale, item and item pair scalability coefficients. Per element accuracy, scalability coefficients, and confidence intervals around scalability coefficients are sensitive to sample size. The results from Straat et al. were not replicated; depending on the main goal of the research, sample sizes ranging from > 250 to > 1000 are needed. Using our pragmatic approach, some practical recommendations are made regarding sample sizes for studies of Mokken scaling.