Application of bayesian methodology to measure equivalence between two rating scales.

Background: 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.

Objective: 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).

Methods: 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.

Results: 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.

Discussion: 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.