Construct validation of a modified differentiation index

Abstract

This study assessed the validity of Holland's differentiation construct. Three measures were hypothesized to be related to the ability to make, and ease of making, vocational decisions, and the stability of those decisions: differentiation indices, the vocational identity scale from the My Vocational Situation, and the Occupational Alternatives Question (OAQ). An alternative to the traditional method of calculating differentiation was proposed. A modified differentiation index correlated significantly with both vocational identity and OAQ scores; the traditional index did not. Results indicated that the traditional differentiation index is not a useful way of approaching the differentiation construct. The results are discussed in the context of operationalizing the differentiation construct in a way which more closely reflects its conceptual definition.