Validation of a questionnaire used to assess safety and professionalism among arborists

This article summarizes a validation study of an instrument designed to measure safety and professionalism practices of arborists. A sample of 386 arborists from the State of Louisiana responded to the 58-item questionnaire. Analyses focused on several aspects of Messick's validation framework. Structural validity evidence was provided by analyses that indicate that the measures are unidimensional. Content validity evidence was supported by generally high positive values of the biserial correlations and optimal values of standardized mean-square item fit indices. Substantive validity evidence was provided by analyses that support the use of the two-point rating scale and a rank ordering of item means that is consistent with substantive theory. Person fit indices indicated little misfit among measures. Support for the generalizability aspect of validity was provided by an acceptable level of internal consistency and fairly tight error bands around estimated arborist measures. Additionally, few items exhibited DIF. Finally, with respect to the external aspect of validity, group differences between arborist measures were consistent with substantive theory.