Application of bayesian methodology to measure equivalence between two rating scales

Little is known about measuring equivalence between two rating scales. Measuring the equivalence between two rating scales requires a study design and analysis conducive to clear interpretation of actual equivalence with simple inferences.

The aim of this study was to show the use of bayesian methodology in determining equivalence within a simulated content validity study (to establish equivalence, not content validity).

Participants were randomized into two groups and responded to the items' perceived relevance or perceived correlation to a construct, job enjoyment. Items from the National Database of Nursing Quality Indicators were used.

Eighty-seven nursing faculty members from various schools of nursing participated. Findings revealed in all items having a posterior probability of >95% that rating scales are equivalent using an informative prior whereas using a weak or flat prior led to a minimal decrease in posterior probability results.

Prior and new information collected from this study was used to determine a posterior probability that a mean difference (±0.5 points) between the relevance and correlation group exists, thereby demonstrating equivalence between two rating scales.